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CVE-2026-31429— net: skb: fix cross-cache free of KFENCE-allocated skb head

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于skb_kfree_head函数可能错误地将KFENCE分配的对象释放到错误的缓存，导致跨缓存释放问题。

AI Predicted 5.5 Difficulty: Theoretical EPSS 0.16% · P5

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 12

VendorProduct Version RangeStatus
Linux Linux bf9f1baa279f0758dc2297080360c5a616843927< 128b03ccb2582a643983a48a37fda58df80edbde affected
bf9f1baa279f0758dc2297080360c5a616843927< 60313768a8edc7094435975587c00c2d7b834083 affected
bf9f1baa279f0758dc2297080360c5a616843927< 2d64618ea846d8d033477311f805ca487d6a6696 affected
bf9f1baa279f0758dc2297080360c5a616843927< 474e00b935db250cac320d10c1d3cf4e44b46721 affected
bf9f1baa279f0758dc2297080360c5a616843927< 0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516 affected
6.3 affected
< 6.3 unaffected
6.6.136≤ 6.6.* unaffected
… +4 more rows
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I. Basic Information for CVE-2026-31429

Vulnerability Information
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Vulnerability Title
net: skb: fix cross-cache free of KFENCE-allocated skb head
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于skb_kfree_head函数可能错误地将KFENCE分配的对象释放到错误的缓存，导致跨缓存释放问题。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux bf9f1baa279f0758dc2297080360c5a616843927 ~ 128b03ccb2582a643983a48a37fda58df80edbde -
Linux Linux 6.3 -

II. Public POCs for CVE-2026-31429

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III. Intelligence Information for CVE-2026-31429

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Patches & Fixes for CVE-2026-31429 (1)

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-31429

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