Vulnerability-Lookup

FKIE_CVE-2020-36791

Vulnerability from fkie_nvd - Published: 2025-05-07 14:15 - Updated: 2026-08-04 10:16

Severity

7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.1 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

Summary

In the Linux kernel, the following vulnerability has been resolved: net_sched: keep alloc_hash updated after hash allocation In commit 599be01ee567 ("net_sched: fix an OOB access in cls_tcindex") I moved cp->hash calculation before the first tcindex_alloc_perfect_hash(), but cp->alloc_hash is left untouched. This difference could lead to another out of bound access. cp->alloc_hash should always be the size allocated, we should update it after this tcindex_alloc_perfect_hash().

References

URL	Tags
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://blog.cdthoughts.ch/2021/03/16/syzbot-bug.html	Third Party Advisory
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/0d1c3530e1bd38382edef72591b78e877e0edcd3	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/557d015ffb27b672e24e6ad141fd887783871dc2	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/9f8b6c44be178c2498a00b270872a6e30e7c8266	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/bd3ee8fb6371b45c71c9345cc359b94da2ddefa9	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/c4453d2833671e3a9f6bd52f0f581056c3736386	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/d23faf32e577922b6da20bf3740625c1105381bf	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/d6cdc5bb19b595486fb2e6661e5138d73a57f454	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://syzkaller.appspot.com/bug?id=ea260693da894e7b078d18fca2c9c0a19b457534	Issue Tracking

Impacted products

Vendor	Product	Version
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	5.6
linux	linux_kernel	5.6
linux	linux_kernel	5.6
linux	linux_kernel	5.6
linux	linux_kernel	5.6
linux	linux_kernel	5.6
linux	linux_kernel	5.6

JSON

To clipboard

{
  "affected": [
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      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet_sched: keep alloc_hash updated after hash allocation\n\nIn commit 599be01ee567 (\"net_sched: fix an OOB access in cls_tcindex\")\nI moved cp-\u003ehash calculation before the first\ntcindex_alloc_perfect_hash(), but cp-\u003ealloc_hash is left untouched.\nThis difference could lead to another out of bound access.\n\ncp-\u003ealloc_hash should always be the size allocated, we should\nupdate it after this tcindex_alloc_perfect_hash()."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: net_sched: mantener alloc_hash actualizado tras la asignaci\u00f3n de hash. En el commit 599be01ee567 (\"net_sched: corregir un acceso OOB en cls_tcindex\"), se movi\u00f3 el c\u00e1lculo de cp-\u0026gt;hash antes del primer tcindex_alloc_perfect_hash(), pero se mantuvo intacto. Esta diferencia podr\u00eda provocar otro acceso fuera de los l\u00edmites. cp-\u0026gt;alloc_hash siempre debe tener el tama\u00f1o asignado; debemos actualizarlo despu\u00e9s de este tcindex_alloc_perfect_hash()."
    }
  ],
  "id": "CVE-2020-36791",
  "lastModified": "2026-08-04T10:16:35.580",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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        "impactScore": 5.2,
        "source": "nvd@nist.gov",
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  "published": "2025-05-07T14:15:28.513",
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      "url": "https://blog.cdthoughts.ch/2021/03/16/syzbot-bug.html"
    },
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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  "vulnStatus": "Modified",
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          "value": "CWE-125"
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      "source": "nvd@nist.gov",
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}

CVE-2020-36791 (GCVE-0-2020-36791)

Vulnerability from cvelistv5 – Published: 2025-05-07 13:17 – Updated: 2026-08-05 08:44

Title

net_sched: keep alloc_hash updated after hash allocation

Summary

Severity

7.8 (High)


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

Assigner

Linux mitre root

References

9 references

URL	Tags
https://git.kernel.org/stable/c/d6cdc5bb19b595486…
https://git.kernel.org/stable/c/c4453d2833671e3a9…
https://git.kernel.org/stable/c/9f8b6c44be178c249…
https://git.kernel.org/stable/c/557d015ffb27b672e…
https://git.kernel.org/stable/c/d23faf32e577922b6…
https://git.kernel.org/stable/c/bd3ee8fb6371b45c7…
https://git.kernel.org/stable/c/0d1c3530e1bd38382…
https://syzkaller.appspot.com/bug?id=ea260693da89…
https://blog.cdthoughts.ch/2021/03/16/syzbot-bug.html

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 73c29d2f6f8ae731b1e09051b69ed3ba2319482b , < d6cdc5bb19b595486fb2e6661e5138d73a57f454 (git) Affected: b974ac51f5834a729de252fc5c1c9de9efd79b45 , < c4453d2833671e3a9f6bd52f0f581056c3736386 (git) Affected: 6cb448ee493c8a514c9afa0c346f3f5b3227de85 , < 9f8b6c44be178c2498a00b270872a6e30e7c8266 (git) Affected: 478c4b2ffd44e5186c7e22ae7c38a86a5b9cfde5 , < 557d015ffb27b672e24e6ad141fd887783871dc2 (git) Affected: dd8142a6fa5270783d415292ec8169f4ea2a5468 , < d23faf32e577922b6da20bf3740625c1105381bf (git) Affected: 2c66ff8d08f81bcf8e8cb22e31e39c051b15336a , < bd3ee8fb6371b45c71c9345cc359b94da2ddefa9 (git) Affected: 599be01ee567b61f4471ee8078870847d0a11e8e , < 0d1c3530e1bd38382edef72591b78e877e0edcd3 (git)
Linux	Linux	Affected: 4.4.214 , < 4.4.218 (semver) Affected: 4.9.214 , < 4.9.218 (semver) Affected: 4.14.171 , < 4.14.175 (semver) Affected: 4.19.103 , < 4.19.114 (semver) Affected: 5.4.19 , < 5.4.29 (semver) Affected: 5.5.3 , < 5.5.14 (semver)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
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        {
          "defaultStatus": "unaffected",
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          "programFiles": [
            "net/sched/cls_tcindex.c"
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "4.19.114",
                  "versionStartIncluding": "4.19.103",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.4.29",
                  "versionStartIncluding": "5.4.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.5.14",
                  "versionStartIncluding": "5.5.3",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet_sched: keep alloc_hash updated after hash allocation\n\nIn commit 599be01ee567 (\"net_sched: fix an OOB access in cls_tcindex\")\nI moved cp-\u003ehash calculation before the first\ntcindex_alloc_perfect_hash(), but cp-\u003ealloc_hash is left untouched.\nThis difference could lead to another out of bound access.\n\ncp-\u003ealloc_hash should always be the size allocated, we should\nupdate it after this tcindex_alloc_perfect_hash()."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is triggered through the tc filter netlink configuration path (RTM_NEWTFILTER \u2192 tc_new_tfilter \u2192 tcindex_change \u2192 tcindex_set_parms), not by processing network packets. Exploitation requires local netlink/syscall access to configure cls_tcindex.\nAC:L - An attacker fully controls both the old and new hash sizes and the filter handle via netlink attributes, so shrinking a perfect hash while using a handle past the newly allocated size reliably produces the OOB access with no race or external conditions.\nPR:L - tc_new_tfilter requires CAP_NET_ADMIN checked with netlink_ns_capable against the network namespace\u0027s user_ns, which an unprivileged user can obtain via user namespaces (unshare -Urn) without real root in the init namespace.\nUI:N - The attacker creates and modifies their own tcindex filters in a network namespace they control; no victim action is required.\nS:U - Impact is confined to the host kernel privilege boundary (local memory corruption / privilege escalation) and does not cross VM, IOMMU, or other distinct security authorities.\nC:H - Stale alloc_hash allows OOB reads through tcindex_get/tcindex_lookup (perfect + handle beyond the allocated array), and the heap OOB can be leveraged for arbitrary kernel memory disclosure.\nI:H - tcindex_set_parms does r = cp-\u003eperfect + handle then writes result/exts into that slot; with handle past the newly allocated hash this is a controlled heap out-of-bounds write enabling memory corruption and control-flow hijacking.\nA:H - The out-of-bounds access was caught by syzbot as a kernel memory-safety failure and can produce oops/panic or heap corruption leading to a crash even without full exploitation."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T08:44:33.087Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/d6cdc5bb19b595486fb2e6661e5138d73a57f454"
        },
        {
          "url": "https://git.kernel.org/stable/c/c4453d2833671e3a9f6bd52f0f581056c3736386"
        },
        {
          "url": "https://git.kernel.org/stable/c/9f8b6c44be178c2498a00b270872a6e30e7c8266"
        },
        {
          "url": "https://git.kernel.org/stable/c/557d015ffb27b672e24e6ad141fd887783871dc2"
        },
        {
          "url": "https://git.kernel.org/stable/c/d23faf32e577922b6da20bf3740625c1105381bf"
        },
        {
          "url": "https://git.kernel.org/stable/c/bd3ee8fb6371b45c71c9345cc359b94da2ddefa9"
        },
        {
          "url": "https://git.kernel.org/stable/c/0d1c3530e1bd38382edef72591b78e877e0edcd3"
        },
        {
          "url": "https://syzkaller.appspot.com/bug?id=ea260693da894e7b078d18fca2c9c0a19b457534"
        },
        {
          "url": "https://blog.cdthoughts.ch/2021/03/16/syzbot-bug.html"
        }
      ],
      "title": "net_sched: keep alloc_hash updated after hash allocation",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2020-36791",
    "datePublished": "2025-05-07T13:17:33.882Z",
    "dateReserved": "2024-02-26T17:07:27.435Z",
    "dateUpdated": "2026-08-05T08:44:33.087Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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.
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.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

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.