CVE-2026-31641
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk4th percentile - higher than 4% of all known CVEs
Summary
In the Linux kernel's RxRPC subsystem, a heap buffer overflow vulnerability was found in RxGK token loading. The function rxrpc_preparse_xdr_yfs_rxgk() incorrectly rounds key and ticket lengths, causing values >= 0xfffffffd to wrap to zero and bypass validation, allowing ~4 GB of data to be copied into a small buffer. The flaw can be triggered by an unprivileged user via the add_key() syscall.
Risk Assessment
The organization faces local privilege escalation or system crash (kernel panic) due to heap buffer overflow. An unprivileged attacker can compromise kernel memory integrity, potentially leading to privilege escalation.
Recommendation
Apply the security patch from the Linux kernel distributor addressing CVE-2026-31641 immediately. Update the kernel to a version containing the fix commit.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: rxrpc: Fix RxGK token loading to check bounds rxrpc_preparse_xdr_yfs_rxgk() reads the raw key length and ticket length from the XDR token as u32 values and passes each through round_up(x, 4) before using the rounded value for validation and allocation. When the raw length is >= 0xfffffffd, round_up() wraps to 0, so the bounds check and kzalloc both use 0 while the subsequent memcpy still copies the original ~4 GiB value, producing a heap buffer overflow reachable from an unprivileged add_key() call. Fix this by: (1) Rejecting raw key lengths above AFSTOKEN_GK_KEY_MAX and raw ticket lengths above AFSTOKEN_GK_TOKEN_MAX before rounding, consistent with the caps that the RxKAD path already enforces via AFSTOKEN_RK_TIX_MAX. (2) Sizing the flexible-array allocation from the validated raw key length via struct_size_t() instead of the rounded value. (3) Caching the raw lengths so that the later field assignments and memcpy calls do not re-read from the token, eliminating a class of TOCTOU re-parse. The control path (valid token with lengths within bounds) is unaffected.