Vulnerability-Lookup

FKIE_CVE-2026-31429

Vulnerability from fkie_nvd - Published: 2026-04-20 10:16 - Updated: 2026-06-17 10:33

Severity

5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Summary

In the Linux kernel, the following vulnerability has been resolved: net: skb: fix cross-cache free of KFENCE-allocated skb head SKB_SMALL_HEAD_CACHE_SIZE is intentionally set to a non-power-of-2 value (e.g. 704 on x86_64) to avoid collisions with generic kmalloc bucket sizes. This ensures that skb_kfree_head() can reliably use skb_end_offset to distinguish skb heads allocated from skb_small_head_cache vs. generic kmalloc caches. However, when KFENCE is enabled, kfence_ksize() returns the exact requested allocation size instead of the slab bucket size. If a caller (e.g. bpf_test_init) allocates skb head data via kzalloc() and the requested size happens to equal SKB_SMALL_HEAD_CACHE_SIZE, then slab_build_skb() -> ksize() returns that exact value. After subtracting skb_shared_info overhead, skb_end_offset ends up matching SKB_SMALL_HEAD_HEADROOM, causing skb_kfree_head() to incorrectly free the object to skb_small_head_cache instead of back to the original kmalloc cache, resulting in a slab cross-cache free: kmem_cache_free(skbuff_small_head): Wrong slab cache. Expected skbuff_small_head but got kmalloc-1k Fix this by always calling kfree(head) in skb_kfree_head(). This keeps the free path generic and avoids allocator-specific misclassification for KFENCE objects.

References

URL	Tags
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/128b03ccb2582a643983a48a37fda58df80edbde	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/2d64618ea846d8d033477311f805ca487d6a6696	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/474e00b935db250cac320d10c1d3cf4e44b46721	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/60313768a8edc7094435975587c00c2d7b834083	Patch

Impacted products

Vendor	Product	Version
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	7.0
linux	linux_kernel	7.0
linux	linux_kernel	7.0
linux	linux_kernel	7.0
linux	linux_kernel	7.0
linux	linux_kernel	7.0
linux	linux_kernel	7.0

JSON

To clipboard

{
  "affected": [
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      "affectedData": [
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          "product": "Linux",
          "programFiles": [
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  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: skb: fix cross-cache free of KFENCE-allocated skb head\n\nSKB_SMALL_HEAD_CACHE_SIZE is intentionally set to a non-power-of-2\nvalue (e.g. 704 on x86_64) to avoid collisions with generic kmalloc\nbucket sizes. This ensures that skb_kfree_head() can reliably use\nskb_end_offset to distinguish skb heads allocated from\nskb_small_head_cache vs. generic kmalloc caches.\n\nHowever, when KFENCE is enabled, kfence_ksize() returns the exact\nrequested allocation size instead of the slab bucket size. If a caller\n(e.g. bpf_test_init) allocates skb head data via kzalloc() and the\nrequested size happens to equal SKB_SMALL_HEAD_CACHE_SIZE, then\nslab_build_skb() -\u003e ksize() returns that exact value. After subtracting\nskb_shared_info overhead, skb_end_offset ends up matching\nSKB_SMALL_HEAD_HEADROOM, causing skb_kfree_head() to incorrectly free\nthe object to skb_small_head_cache instead of back to the original\nkmalloc cache, resulting in a slab cross-cache free:\n\n  kmem_cache_free(skbuff_small_head): Wrong slab cache. Expected\n  skbuff_small_head but got kmalloc-1k\n\nFix this by always calling kfree(head) in skb_kfree_head(). This keeps\nthe free path generic and avoids allocator-specific misclassification\nfor KFENCE objects."
    }
  ],
  "id": "CVE-2026-31429",
  "lastModified": "2026-06-17T10:33:42.150",
  "metrics": {
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          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 5.5,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 3.6,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
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  "published": "2026-04-20T10:16:16.737",
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  "vulnStatus": "Analyzed",
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          "lang": "en",
          "value": "CWE-401"
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      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
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  ]
}

CVE-2026-31429 (GCVE-0-2026-31429)

Vulnerability from cvelistv5 – Published: 2026-04-20 09:43 – Updated: 2026-05-11 22:08

Title

net: skb: fix cross-cache free of KFENCE-allocated skb head

Summary

Severity

No CVSS data available.

Assigner

Linux mitre root

References

5 references

URL	Tags
https://git.kernel.org/stable/c/128b03ccb2582a643…
https://git.kernel.org/stable/c/60313768a8edc7094…
https://git.kernel.org/stable/c/2d64618ea846d8d03…
https://git.kernel.org/stable/c/474e00b935db250ca…
https://git.kernel.org/stable/c/0f42e3f4fe2a58394…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 128b03ccb2582a643983a48a37fda58df80edbde (git) Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 60313768a8edc7094435975587c00c2d7b834083 (git) Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 2d64618ea846d8d033477311f805ca487d6a6696 (git) Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 474e00b935db250cac320d10c1d3cf4e44b46721 (git) Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516 (git)
Linux	Linux	Affected: 6.3 Unaffected: 0 , < 6.3 (semver) Unaffected: 6.6.136 , ≤ 6.6.* (semver) Unaffected: 6.12.82 , ≤ 6.12.* (semver) Unaffected: 6.18.23 , ≤ 6.18.* (semver) Unaffected: 6.19.13 , ≤ 6.19.* (semver) Unaffected: 7.0 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/core/skbuff.c"
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        }
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        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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        {
          "url": "https://git.kernel.org/stable/c/0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516"
        }
      ],
      "title": "net: skb: fix cross-cache free of KFENCE-allocated skb head",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-31429",
    "datePublished": "2026-04-20T09:43:03.194Z",
    "dateReserved": "2026-03-09T15:48:24.089Z",
    "dateUpdated": "2026-05-11T22:08:32.321Z",
    "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.