Vulnerability-Lookup

GHSA-GX83-3VF8-GH7J

Vulnerability from github – Published: 2026-09-28 20:44 – Updated: 2026-09-28 20:44

Summary

jackson-databind: Comparable missing from DefaultBaseTypeLimitingValidator's unsafe base types (incomplete PolymorphicTypeValidator denylist)

Details

Summary

DefaultBaseTypeLimitingValidator — the PolymorphicTypeValidator used automatically whenever @JsonTypeInfo is applied without an explicitly configured custom validator — denies polymorphic resolution only for nine specific "unsafe base types" (Object, Serializable, Closeable, AutoCloseable, Cloneable, Runnable, java.util.logging.Handler, javax.naming.Referenceable, javax.sql.DataSource). Its isSafeSubType() returns true unconditionally for every other base type. java.lang.Comparable is not in that list, despite being implemented by a very large fraction of JDK and application classes — comparable in breadth to Serializable, which is denylisted for exactly that reason. An application with an @JsonTypeInfo-annotated Comparable-typed property, and no custom validator configured, will accept a type identifier for essentially any class implementing Comparable.

Details

Affected file: src/main/java/tools/jackson/databind/jsontype/DefaultBaseTypeLimitingValidator.java

private final static class UnsafeBaseTypes {
    private final Set<String> UNSAFE = new HashSet<>();
    {
        UNSAFE.add(Object.class.getName());
        UNSAFE.add(java.io.Closeable.class.getName());
        UNSAFE.add(java.io.Serializable.class.getName());
        UNSAFE.add(AutoCloseable.class.getName());
        UNSAFE.add(Cloneable.class.getName());
        UNSAFE.add(Runnable.class.getName());          // [databind#5014]
        UNSAFE.add("java.util.logging.Handler");
        UNSAFE.add("javax.naming.Referenceable");
        UNSAFE.add("javax.sql.DataSource");
        // java.lang.Comparable is NOT present here
    }
}

protected boolean isSafeSubType(DatabindContext ctxt,
        JavaType baseType, JavaType subType) {
    return true;   // unconditional for every base type not in UNSAFE
}

The class's own JavaDoc acknowledges the design ("Note that when using potentially unsafe base type like java.lang.Object a custom implementation... is needed"), so the trade-off of leaving broad base types unrestricted is intentional. The gap is that Comparable has the same breadth of implementers as the types this class does restrict, and its absence looks like an oversight rather than a deliberate choice — consistent with the ongoing, incremental nature of this list (Runnable was added recently for issue #5014).

This is specific to the default, unconfigured validator reached via bare @JsonTypeInfo usage. Global "Default Typing" via activateDefaultTyping() is not affected, because that method structurally requires an explicit PolymorphicTypeValidator argument — a correctly-configured BasicPolymorphicTypeValidator rejects the same payload under activateDefaultTyping().

PoC

Built entirely from source (jackson-databind + jackson-core + jackson-annotations, javac, OpenJDK 21, no third-party gadget libraries, no network access):

1. Sanity check (benign class, confirms the mechanism fires):

static class SafeThing implements Comparable<SafeThing> {
    public String name;
    public SafeThing() {}
    public int compareTo(SafeThing o) { return 0; }
}
static class Holder {
    @JsonTypeInfo(use = JsonTypeInfo.Id.CLASS)
    public Comparable<?> value;
}

ObjectMapper mapper = JsonMapper.builder().build();   // no custom PTV
String json = "{\"value\":{\"@class\":\"...SafeThing\",\"name\":\"hello\"}}";
Holder h = mapper.readValue(json, Holder.class);
// RESULT: ACCEPTED, class=...SafeThing

2. Real JDK class substitution:

String json = "{\"value\":[\"java.io.File\",\"/etc/passwd\"]}";
Holder h = mapper.readValue(json, Holder.class);
// RESULT: ACCEPTED, class=java.io.File value=/etc/passwd

3. Negative control — Default Typing with an explicit custom PTV:

PolymorphicTypeValidator ptv = BasicPolymorphicTypeValidator.builder()
    .allowIfSubType("PtvGapTest4").build();
ObjectMapper mapper = JsonMapper.builder()
    .activateDefaultTyping(ptv, DefaultTyping.NON_FINAL).build();
// same java.io.File payload
// RESULT: REJECTED - InvalidTypeIdException: "...denied resolution"

Observed output:

$ java -cp .:build/classes PtvGapTest3 Trying: {"value":["java.io.File","/etc/passwd"]} ACCEPTED, class=java.io.File value=/etc/passwd

$ java -cp .:build/classes PtvGapTest4 Trying malicious substitution: ["PtvGapTest4$Holder",{"value":["java.io.File","/etc/passwd"]}] REJECTED - InvalidTypeIdException: Could not resolve type id 'java.io.File' as a subtype of java.lang.Comparable: Configured PolymorphicTypeValidator denied resolution

Impact

Any application declaring an @JsonTypeInfo-annotated property or class with Comparable as its base type, without a separately configured restrictive PolymorphicTypeValidator, will accept a type identifier for essentially any class implementing Comparable. Concrete impact is demonstrated via java.io.File: an attacker can cause construction of a File object for an arbitrary, attacker-chosen path. On its own this is a controlled-object-instantiation primitive; if the application later calls path-sensitive or mutating methods on the received value, this becomes a path-traversal-adjacent primitive.

Suggested remediation: 1. Add java.lang.Comparable to UnsafeBaseTypes.UNSAFE. 2. Audit other broad JDK interfaces (java.lang.Iterable, java.util.EventListener) for the same gap. 3. Consider a narrower default for isSafeSubType() for base types outside the fixed denylist, rather than unconditional true.

Severity

5.6 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

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JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Maven",
        "name": "tools.jackson.core:jackson-databind"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
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              "fixed": "3.1.6"
            }
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    {
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        "name": "com.fasterxml.jackson.core:jackson-databind"
      },
      "ranges": [
        {
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            {
              "introduced": "2.11.0"
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            }
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        "ecosystem": "Maven",
        "name": "com.fasterxml.jackson.core:jackson-databind"
      },
      "ranges": [
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            }
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          "type": "ECOSYSTEM"
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      "package": {
        "ecosystem": "Maven",
        "name": "com.fasterxml.jackson.core:jackson-databind"
      },
      "ranges": [
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          "events": [
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            },
            {
              "fixed": "2.22.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-83557"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-502",
      "CWE-915"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-28T20:44:25Z",
    "nvd_published_at": "2026-09-01T15:17:37Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n`DefaultBaseTypeLimitingValidator` \u2014 the `PolymorphicTypeValidator` used automatically whenever `@JsonTypeInfo` is applied without an explicitly configured custom validator \u2014 denies polymorphic resolution only for nine specific \"unsafe base types\" (`Object`, `Serializable`, `Closeable`, `AutoCloseable`, `Cloneable`, `Runnable`, `java.util.logging.Handler`, `javax.naming.Referenceable`, `javax.sql.DataSource`). Its `isSafeSubType()` returns `true` unconditionally for every other base type. `java.lang.Comparable` is not in that list, despite being implemented by a very large fraction of JDK and application classes \u2014 comparable in breadth to `Serializable`, which is denylisted for exactly that reason. An application with an `@JsonTypeInfo`-annotated `Comparable`-typed property, and no custom validator configured, will accept a type identifier for essentially any class implementing `Comparable`.\n\n### Details\n**Affected file:** `src/main/java/tools/jackson/databind/jsontype/DefaultBaseTypeLimitingValidator.java`\n\n```java\nprivate final static class UnsafeBaseTypes {\n    private final Set\u003cString\u003e UNSAFE = new HashSet\u003c\u003e();\n    {\n        UNSAFE.add(Object.class.getName());\n        UNSAFE.add(java.io.Closeable.class.getName());\n        UNSAFE.add(java.io.Serializable.class.getName());\n        UNSAFE.add(AutoCloseable.class.getName());\n        UNSAFE.add(Cloneable.class.getName());\n        UNSAFE.add(Runnable.class.getName());          // [databind#5014]\n        UNSAFE.add(\"java.util.logging.Handler\");\n        UNSAFE.add(\"javax.naming.Referenceable\");\n        UNSAFE.add(\"javax.sql.DataSource\");\n        // java.lang.Comparable is NOT present here\n    }\n}\n\nprotected boolean isSafeSubType(DatabindContext ctxt,\n        JavaType baseType, JavaType subType) {\n    return true;   // unconditional for every base type not in UNSAFE\n}\n```\n\nThe class\u0027s own JavaDoc acknowledges the design (*\"Note that when using potentially unsafe base type like `java.lang.Object` a custom implementation... is needed\"*), so the trade-off of leaving broad base types unrestricted is intentional. The gap is that `Comparable` has the same breadth of implementers as the types this class *does* restrict, and its absence looks like an oversight rather than a deliberate choice \u2014 consistent with the ongoing, incremental nature of this list (`Runnable` was added recently for issue #5014).\n\nThis is specific to the **default, unconfigured validator** reached via bare `@JsonTypeInfo` usage. Global \"Default Typing\" via `activateDefaultTyping()` is **not** affected, because that method structurally requires an explicit `PolymorphicTypeValidator` argument \u2014 a correctly-configured `BasicPolymorphicTypeValidator` rejects the same payload under `activateDefaultTyping()`.\n\n### PoC\nBuilt entirely from source (jackson-databind + jackson-core + jackson-annotations, `javac`, OpenJDK 21, no third-party gadget libraries, no network access):\n\n**1. Sanity check (benign class, confirms the mechanism fires):**\n```java\nstatic class SafeThing implements Comparable\u003cSafeThing\u003e {\n    public String name;\n    public SafeThing() {}\n    public int compareTo(SafeThing o) { return 0; }\n}\nstatic class Holder {\n    @JsonTypeInfo(use = JsonTypeInfo.Id.CLASS)\n    public Comparable\u003c?\u003e value;\n}\n\nObjectMapper mapper = JsonMapper.builder().build();   // no custom PTV\nString json = \"{\\\"value\\\":{\\\"@class\\\":\\\"...SafeThing\\\",\\\"name\\\":\\\"hello\\\"}}\";\nHolder h = mapper.readValue(json, Holder.class);\n// RESULT: ACCEPTED, class=...SafeThing\n```\n\n**2. Real JDK class substitution:**\n```java\nString json = \"{\\\"value\\\":[\\\"java.io.File\\\",\\\"/etc/passwd\\\"]}\";\nHolder h = mapper.readValue(json, Holder.class);\n// RESULT: ACCEPTED, class=java.io.File value=/etc/passwd\n```\n\n**3. Negative control \u2014 Default Typing with an explicit custom PTV:**\n```java\nPolymorphicTypeValidator ptv = BasicPolymorphicTypeValidator.builder()\n    .allowIfSubType(\"PtvGapTest4\").build();\nObjectMapper mapper = JsonMapper.builder()\n    .activateDefaultTyping(ptv, DefaultTyping.NON_FINAL).build();\n// same java.io.File payload\n// RESULT: REJECTED - InvalidTypeIdException: \"...denied resolution\"\n```\n\n**Observed output:**\n\n\n\n\n$ java -cp .:build/classes PtvGapTest3\nTrying: {\"value\":[\"java.io.File\",\"/etc/passwd\"]}\nACCEPTED, class=java.io.File value=/etc/passwd\n\n$ java -cp .:build/classes PtvGapTest4\nTrying malicious substitution: [\"PtvGapTest4$Holder\",{\"value\":[\"java.io.File\",\"/etc/passwd\"]}]\nREJECTED - InvalidTypeIdException: Could not resolve type id \u0027java.io.File\u0027 as a\nsubtype of java.lang.Comparable: Configured PolymorphicTypeValidator denied resolution\n\n\n\n\n### Impact\nAny application declaring an `@JsonTypeInfo`-annotated property or class with `Comparable` as its base type, without a separately configured restrictive `PolymorphicTypeValidator`, will accept a type identifier for essentially any class implementing `Comparable`. Concrete impact is demonstrated via `java.io.File`: an attacker can cause construction of a `File` object for an arbitrary, attacker-chosen path. On its own this is a controlled-object-instantiation primitive; if the application later calls path-sensitive or mutating methods on the received value, this becomes a path-traversal-adjacent primitive. \n\n**Suggested remediation:**\n1. Add `java.lang.Comparable` to `UnsafeBaseTypes.UNSAFE`.\n2. Audit other broad JDK interfaces (`java.lang.Iterable`, `java.util.EventListener`) for the same gap.\n3. Consider a narrower default for `isSafeSubType()` for base types outside the fixed denylist, rather than unconditional `true`.",
  "id": "GHSA-gx83-3vf8-gh7j",
  "modified": "2026-09-28T20:44:25Z",
  "published": "2026-09-28T20:44:25Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/FasterXML/jackson-databind/security/advisories/GHSA-gx83-3vf8-gh7j"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-83557"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FasterXML/jackson-databind/issues/6156"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FasterXML/jackson-databind/pull/6155"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FasterXML/jackson-databind/commit/eb3b7fc0f9c0d27f471550ac3316b17d1987388f"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/FasterXML/jackson-databind"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FasterXML/jackson-databind/releases/tag/jackson-databind-2.18.10"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FasterXML/jackson-databind/releases/tag/jackson-databind-2.21.6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FasterXML/jackson-databind/releases/tag/jackson-databind-2.22.2"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FasterXML/jackson-databind/releases/tag/jackson-databind-3.1.6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FasterXML/jackson-databind/releases/tag/jackson-databind-3.2.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "jackson-databind: Comparable missing from DefaultBaseTypeLimitingValidator\u0027s unsafe base types (incomplete PolymorphicTypeValidator denylist)"
}

CVE-2026-83557 (GCVE-0-2026-83557)

Vulnerability from cvelistv5 – Published: 2026-09-01 14:57 – Updated: 2026-09-01 17:46

Title

jackson-databind omits java.lang.Comparable from DefaultBaseTypeLimitingValidator's unsafe base types

Summary

DefaultBaseTypeLimitingValidator is the PolymorphicTypeValidator applied automatically whenever @JsonTypeInfo is used without an explicitly configured custom validator. It denies polymorphic resolution only for a fixed set of "unsafe base types", and its isSafeSubType method returns true unconditionally for every base type outside that set. java.lang.Comparable was absent from the list despite being implemented by a very large fraction of JDK and application classes, comparable in breadth to java.io.Serializable, which is on the list for that reason. An application declaring an @JsonTypeInfo-annotated property or class with Comparable as its base type, and no custom PolymorphicTypeValidator, will accept a type identifier for essentially any class implementing Comparable. This yields an attacker-controlled object instantiation primitive; a demonstrated case constructs a java.io.File for an arbitrary attacker-chosen path, which becomes path-traversal-adjacent if the application subsequently calls path-sensitive methods on the value. No class implementing Comparable has been identified that yields code execution through deserialization alone. Global Default Typing via activateDefaultTyping is not affected, because that method structurally requires an explicit PolymorphicTypeValidator argument. This affects com.fasterxml.jackson.core:jackson-databind from 2.11.0 before 2.18.10, from 2.19.0 before 2.21.6, and from 2.22.0 before 2.22.2, and tools.jackson.core:jackson-databind from 3.0.0 before 3.1.6 and from 3.2.0 before 3.2.2. Users should upgrade to 2.18.10, 2.21.6, 2.22.2, 3.1.6, or 3.2.2.

Severity

5.6 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-01 17:46 UTC

CWE

CWE-502 - Deserialization of Untrusted Data
CWE-915 - Improperly Controlled Modification of Dynamically-Determined Object Attributes

Assigner

HeroDevs mitre root

References

4 references

URL	Tags
https://github.com/FasterXML/jackson-databind/sec…	third-party-advisory
https://github.com/FasterXML/jackson-databind/pull/6155	patchissue-tracking
https://github.com/FasterXML/jackson-databind/iss…	issue-tracking
https://github.com/FasterXML/jackson-databind/com…	patch

Impacted products

2 products

Vendor	Product	Version
FasterXML	jackson-databind	Affected: 2.11.0 , < 2.18.10 (maven) Affected: 2.19.0 , < 2.21.6 (maven) Affected: 2.22.0 , < 2.22.2 (maven)
FasterXML	jackson-databind	Affected: 3.0.0 , < 3.1.6 (maven) Affected: 3.2.0 , < 3.2.2 (maven)

Date Public

2026-09-01 00:00

Credits

prvazsahnazarov Tatu Saloranta (cowtowncoder)

Show details on NVD website

JSON

To clipboard

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        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-502",
              "description": "CWE-502 Deserialization of Untrusted Data",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-915",
              "description": "CWE-915 Improperly Controlled Modification of Dynamically-Determined Object Attributes",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-01T14:57:01.340Z",
        "orgId": "36c7be3b-2937-45df-85ea-ca7133ea542c",
        "shortName": "HeroDevs"
      },
      "references": [
        {
          "name": "GHSA-gx83-3vf8-gh7j",
          "tags": [
            "third-party-advisory"
          ],
          "url": "https://github.com/FasterXML/jackson-databind/security/advisories/GHSA-gx83-3vf8-gh7j"
        },
        {
          "name": "FasterXML/jackson-databind#6155",
          "tags": [
            "patch",
            "issue-tracking"
          ],
          "url": "https://github.com/FasterXML/jackson-databind/pull/6155"
        },
        {
          "name": "FasterXML/jackson-databind#6156",
          "tags": [
            "issue-tracking"
          ],
          "url": "https://github.com/FasterXML/jackson-databind/issues/6156"
        },
        {
          "name": "Fix commit (2.x line, forward-merged to 2.21, 2.22 and the 3.x branches)",
          "tags": [
            "patch"
          ],
          "url": "https://github.com/FasterXML/jackson-databind/commit/eb3b7fc0f9c0d27f471550ac3316b17d1987388f"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "\u003cp\u003eUpgrade to jackson-databind 2.18.10, 2.21.6, 2.22.2 (com.fasterxml.jackson.core) or 3.1.6, 3.2.2 (tools.jackson.core). The fix adds java.lang.Comparable to the UnsafeBaseTypes denylist in DefaultBaseTypeLimitingValidator, so polymorphic resolution against a Comparable base type is denied outright. Applications that legitimately need polymorphic handling of a Comparable-typed property must configure an explicit PolymorphicTypeValidator, for example a BasicPolymorphicTypeValidator with an allow-list of permitted subtypes.\u003c/p\u003e"
            }
          ],
          "value": "Upgrade to jackson-databind 2.18.10, 2.21.6, 2.22.2 (com.fasterxml.jackson.core) or 3.1.6, 3.2.2 (tools.jackson.core). The fix adds java.lang.Comparable to the UnsafeBaseTypes denylist in DefaultBaseTypeLimitingValidator, so polymorphic resolution against a Comparable base type is denied outright. Applications that legitimately need polymorphic handling of a Comparable-typed property must configure an explicit PolymorphicTypeValidator, for example a BasicPolymorphicTypeValidator with an allow-list of permitted subtypes."
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "timeline": [
        {
          "lang": "en",
          "time": "2026-08-11T02:58:00.000Z",
          "value": "Fix committed upstream (FasterXML/jackson-databind#6155)"
        },
        {
          "lang": "en",
          "time": "2026-09-01T00:00:00.000Z",
          "value": "GitHub Security Advisory GHSA-gx83-3vf8-gh7j published by the maintainer"
        }
      ],
      "title": "jackson-databind omits java.lang.Comparable from DefaultBaseTypeLimitingValidator\u0027s unsafe base types",
      "workarounds": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "\u003cp\u003eConfigure an explicit restrictive PolymorphicTypeValidator rather than relying on the default validator, or avoid declaring java.lang.Comparable as the base type of an @JsonTypeInfo-annotated property or class. Narrowing the declared base type to an application-specific interface also removes the exposure.\u003c/p\u003e"
            }
          ],
          "value": "Configure an explicit restrictive PolymorphicTypeValidator rather than relying on the default validator, or avoid declaring java.lang.Comparable as the base type of an @JsonTypeInfo-annotated property or class. Narrowing the declared base type to an application-specific interface also removes the exposure."
        }
      ]
    }
  },
  "cveMetadata": {
    "assignerOrgId": "36c7be3b-2937-45df-85ea-ca7133ea542c",
    "assignerShortName": "HeroDevs",
    "cveId": "CVE-2026-83557",
    "datePublished": "2026-09-01T14:57:01.340Z",
    "dateReserved": "2026-08-31T18:32:14.405Z",
    "dateUpdated": "2026-09-01T17:46:40.145Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

GHSA-GX83-3VF8-GH7J

Summary

Details

PoC

Impact

CVE-2026-83557 (GCVE-0-2026-83557)

Tags

Sightings

Nomenclature

Related by attack behaviour