Vulnerability-Lookup

PYSEC-2026-3455

Vulnerability from pysec - Published: 2026-07-14 17:17 - Updated: 2026-07-22 09:57

Details

pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER decoder shared by the CER and DER codecs parses long-form tags by accumulating continuation octets without an upper bound on the tag ID size, allowing a crafted input to force construction of an arbitrarily large integer with CPU cost growing quadratically and to trigger unhandled ValueError exceptions in Python 3.11+ error formatting paths. Any application decoding untrusted BER, CER, or DER input is affected. This issue is fixed in version 0.6.4.

Severity

7.5 (High)


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

Impacted products

Name	purl
pyasn1	pkg:pypi/pyasn1

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {},
      "package": {
        "ecosystem": "PyPI",
        "name": "pyasn1",
        "purl": "pkg:pypi/pyasn1"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.6.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.0.10a",
        "0.0.11a",
        "0.0.12a",
        "0.0.13",
        "0.0.13a",
        "0.0.13b",
        "0.0.6a",
        "0.0.9a",
        "0.1.1",
        "0.1.2",
        "0.1.3",
        "0.1.4",
        "0.1.5",
        "0.1.6",
        "0.1.7",
        "0.1.8",
        "0.1.9",
        "0.2.1",
        "0.2.2",
        "0.2.3",
        "0.3.1",
        "0.3.2",
        "0.3.3",
        "0.3.4",
        "0.3.5",
        "0.3.6",
        "0.3.7",
        "0.4.1",
        "0.4.2",
        "0.4.3",
        "0.4.4",
        "0.4.5",
        "0.4.6",
        "0.4.7",
        "0.4.8",
        "0.5.0",
        "0.5.1",
        "0.6.0",
        "0.6.1",
        "0.6.2",
        "0.6.3"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-59884",
    "GHSA-m4p7-r5rc-7g4j"
  ],
  "details": "pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER decoder shared by the CER and DER codecs parses long-form tags by accumulating continuation octets without an upper bound on the tag ID size, allowing a crafted input to force construction of an arbitrarily large integer with CPU cost growing quadratically and to trigger unhandled ValueError exceptions in Python 3.11+ error formatting paths. Any application decoding untrusted BER, CER, or DER input is affected. This issue is fixed in version 0.6.4.",
  "id": "PYSEC-2026-3455",
  "modified": "2026-07-22T09:57:24.334467Z",
  "published": "2026-07-14T17:17:14.750Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.4"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-m4p7-r5rc-7g4j"
    },
    {
      "type": "FIX",
      "url": "https://github.com/pyasn1/pyasn1/commit/628e36ecbb5277a3f01572ce418ef54271b165a5"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-59884 (GCVE-0-2026-59884)

Vulnerability from cvelistv5 – Published: 2026-07-14 16:41 – Updated: 2026-07-15 13:50

Title

pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs

Summary

Severity

7.5 (High)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-400 - Uncontrolled Resource Consumption

Assigner

GitHub_M

References

3 references

URL	Tags
https://github.com/pyasn1/pyasn1/security/advisor…	x_refsource_CONFIRM
https://github.com/pyasn1/pyasn1/commit/628e36ecb…	x_refsource_MISC
https://github.com/pyasn1/pyasn1/releases/tag/v0.6.4	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
pyasn1	pyasn1	Affected: < 0.6.4

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-59884",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-07-15T13:50:17.314569Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-07-15T13:50:29.814Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "pyasn1",
          "vendor": "pyasn1",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.6.4"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER decoder shared by the CER and DER codecs parses long-form tags by accumulating continuation octets without an upper bound on the tag ID size, allowing a crafted input to force construction of an arbitrarily large integer with CPU cost growing quadratically and to trigger unhandled ValueError exceptions in Python 3.11+ error formatting paths. Any application decoding untrusted BER, CER, or DER input is affected. This issue is fixed in version 0.6.4."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-400",
              "description": "CWE-400: Uncontrolled Resource Consumption",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-14T16:41:10.277Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-m4p7-r5rc-7g4j",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-m4p7-r5rc-7g4j"
        },
        {
          "name": "https://github.com/pyasn1/pyasn1/commit/628e36ecbb5277a3f01572ce418ef54271b165a5",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pyasn1/pyasn1/commit/628e36ecbb5277a3f01572ce418ef54271b165a5"
        },
        {
          "name": "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.4",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.4"
        }
      ],
      "source": {
        "advisory": "GHSA-m4p7-r5rc-7g4j",
        "discovery": "UNKNOWN"
      },
      "title": "pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-59884",
    "datePublished": "2026-07-14T16:41:10.277Z",
    "dateReserved": "2026-07-07T16:40:07.982Z",
    "dateUpdated": "2026-07-15T13:50:29.814Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

GHSA-M4P7-R5RC-7G4J

Vulnerability from github – Published: 2026-07-21 19:10 – Updated: 2026-07-21 19:10

Summary

pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs

Details

Impact

The BER decoder (shared by the CER and DER codecs) parses long-form tags by accumulating continuation octets in a loop with no upper bound on the size of the tag ID. A crafted input can force the decoder to build an arbitrarily large integer, with CPU cost growing quadratically in input size — a ~1 MB input consumes over a minute of CPU. On Python 3.11+, the oversized tag ID can also trigger an unhandled ValueError (integer string conversion limit) while the decoder formats error messages, violating the documented PyAsn1Error contract and potentially bypassing caller error handling.

Any application decoding untrusted BER/CER/DER input is affected.

Affected components

pyasn1.codec.ber.decoder — decode() and StreamingDecoder
pyasn1.codec.cer.decoder and pyasn1.codec.der.decoder, which inherit the same tag parsing
pyasn1.type.tag — Tag/TagSet reprs could raise ValueError when rendering oversized tag IDs (reachable through decoder error paths)

The encoders and the pyasn1.codec.native codec are not affected.

Patches

Fixed in 0.6.4. Long-form tag IDs are now limited to 20 octets (140-bit tag IDs, matching the existing OID arc limit); oversized tags are rejected with PyAsn1Error. Tag ID rendering in reprs and error messages was additionally hardened against the interpreter's integer-to-string conversion limit.

Workarounds

Bound the size of untrusted input passed to decode() before calling it.

Severity

7.5 (High)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.6.3"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "pyssn1"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.6.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-59884"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-21T19:10:11Z",
    "nvd_published_at": "2026-07-14T17:17:14Z",
    "severity": "HIGH"
  },
  "details": "### Impact\nThe BER decoder (shared by the CER and DER codecs) parses long-form tags by accumulating continuation octets in a loop with no upper bound on the size of the tag ID. A crafted input can force the decoder to build an arbitrarily large integer, with CPU cost growing quadratically in input size \u2014 a ~1 MB input consumes over a minute of CPU. On Python 3.11+, the oversized tag ID can also trigger an unhandled `ValueError` (integer string conversion limit) while the decoder formats error messages, violating the documented `PyAsn1Error` contract and potentially bypassing caller error handling.\n\nAny application decoding untrusted BER/CER/DER input is affected.\n\n### Affected components\n- `pyasn1.codec.ber.decoder` \u2014 `decode()` and `StreamingDecoder`\n- `pyasn1.codec.cer.decoder` and `pyasn1.codec.der.decoder`, which inherit\n  the same tag parsing\n- `pyasn1.type.tag` \u2014 `Tag`/`TagSet` reprs could raise `ValueError` when\n  rendering oversized tag IDs (reachable through decoder error paths)\n\nThe encoders and the `pyasn1.codec.native` codec are not affected.\n\n### Patches\nFixed in 0.6.4. Long-form tag IDs are now limited to 20 octets (140-bit tag IDs, matching the existing OID arc limit); oversized tags are rejected with `PyAsn1Error`. Tag ID rendering in reprs and error messages was additionally hardened against the interpreter\u0027s integer-to-string conversion limit.\n\n### Workarounds\nBound the size of untrusted input passed to `decode()` before calling it.",
  "id": "GHSA-m4p7-r5rc-7g4j",
  "modified": "2026-07-21T19:10:11Z",
  "published": "2026-07-21T19:10:11Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-m4p7-r5rc-7g4j"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-59884"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pyasn1/pyasn1/commit/628e36ecbb5277a3f01572ce418ef54271b165a5"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/pyasn1/pyasn1"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

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.

Action not permitted

PYSEC-2026-3455

CVE-2026-59884 (GCVE-0-2026-59884)

GHSA-M4P7-R5RC-7G4J

Impact

Affected components

Patches

Workarounds

Tags

Sightings

Nomenclature