CVE-2026-31429
net: skb: fix cross-cache free of KFENCE-allocated skb head
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.
INFO
Published Date :
April 20, 2026, 10:16 a.m.
Last Modified :
April 27, 2026, 2:16 p.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Solution
- Always call kfree(head) in skb_kfree_head().
- Ensure consistent deallocation for KFENCE-allocated objects.
- Update the Linux kernel to the latest patched version.
Public PoC/Exploit Available at Github
CVE-2026-31429 has a 3 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-31429.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-31429 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-31429
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
SELinux/IdM proof of concept for confining privileged automation identities and blocking exploit surfaces such as Copy Fail with AAP-aware policy gates.
af-alg ansible ansible-automation-platform automation-security bpf-lsm copyfail exploit-mitigation freeipa github-pages idm red-hat rhel security-hardening selinux
Makefile Shell Python
POC for CVE-2026-31429 (Linux Kernel >= 6.3 < 6.12.82 Slab Cross-Cache Confusion) - vulnerability discovered by Antonius - w1sdom - bluedragonsec.com
C
📡 PoC auto collect from GitHub. ⚠️ Be careful Malware.
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The following list is the news that have been mention
CVE-2026-31429 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-31429 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Apr. 27, 2026
Action Type Old Value New Value Added Reference https://git.kernel.org/stable/c/128b03ccb2582a643983a48a37fda58df80edbde -
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Apr. 20, 2026
Action Type Old Value New Value Added 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. Added Reference https://git.kernel.org/stable/c/0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516 Added Reference https://git.kernel.org/stable/c/2d64618ea846d8d033477311f805ca487d6a6696 Added Reference https://git.kernel.org/stable/c/474e00b935db250cac320d10c1d3cf4e44b46721 Added Reference https://git.kernel.org/stable/c/60313768a8edc7094435975587c00c2d7b834083