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Linux Kernel EUVDEUVD-2026-25534

| CVE-2026-31641 HIGH
Out-of-bounds Read (CWE-125)
2026-04-24 Linux GHSA-p4pm-x7ch-5mvc
Buffer Overflow Linux Information Disclosure
7.8
CVSS 3.1 · Vendor: Linux
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Severity by source

Vendor (Linux) PRIMARY
7.8 HIGH
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SUSE
HIGH
qualitative
Red Hat
7.3 HIGH
qualitative

Primary rating from Vendor (Linux).

CVSS VectorVendor: Linux

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

8
Re-analysis Queued
Apr 27, 2026 - 20:22 vuln.today
cvss_changed
Patch released
Apr 27, 2026 - 20:20 nvd
Patch available
Analysis Generated
Apr 27, 2026 - 15:40 vuln.today
CVSS changed
Apr 27, 2026 - 15:22 NVD
7.8 (HIGH)
Patch available
Apr 24, 2026 - 16:16 EUVD
EUVD ID Assigned
Apr 24, 2026 - 15:00 euvd
EUVD-2026-25534
Analysis Generated
Apr 24, 2026 - 15:00 vuln.today
CVE Published
Apr 24, 2026 - 14:44 nvd
HIGH 7.8

DescriptionCVE.org

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.

AnalysisAI

Heap buffer overflow in Linux kernel rxrpc subsystem allows local authenticated users to trigger memory corruption via crafted RxGK tokens. Exploitable through unprivileged add_key() system call when raw key/ticket lengths >= 0xfffffffd cause integer wraparound in round_up(), bypassing bounds checks while memcpy() copies up to 4 GiB into zero-sized heap allocation. Vendor patches available for stable branches 6.18.23, 6.19.13, and mainline 7.0. EPSS score of 0.02% (4th percentile) indicates low observed exploitation probability despite local privilege escalation potential with CVSS 7.8.

Technical ContextAI

The vulnerability resides in rxrpc_preparse_xdr_yfs_rxgk(), part of the Linux kernel's RxRPC protocol implementation used for AFS (Andrew File System) authentication. RxGK (Rx Generic Kerberos) is a cryptographic framework for securing RxRPC connections. The function parses XDR-encoded tokens containing key material and Kerberos tickets. When processing u32 length fields from untrusted user input via the add_key() syscall, the code applies round_up(x, 4) for alignment before validation. For input values >= 0xfffffffd, this macro wraps to 0 due to integer overflow (0xfffffffd + 3 = 0x100000000, truncated to 0 in 32-bit arithmetic). The wrapped value passes bounds checks and allocates a zero-byte buffer via kzalloc(), but subsequent memcpy() still uses the original multi-gigabyte length value, writing far beyond allocated heap memory. The CPE strings indicate this affects multiple Linux kernel version ranges, with fixes applied across stable series 6.18.x, 6.19.x, and mainline 7.0+.

RemediationAI

Apply vendor-released patches immediately for affected kernel versions: upgrade to Linux 6.18.23 or later for 6.18.x series (commit 3e04596cba8a), upgrade to 6.19.13 or later for 6.19.x series (commit 49875b360c2b), or upgrade to 7.0 or later for mainline kernels (commit d179a868dd75). Patches available from https://git.kernel.org/stable/c/3e04596cba8a86cbff9c3f4bf0a524a3a488773c, https://git.kernel.org/stable/c/49875b360c2b83a3c226e189c502e501d83e6445, and https://git.kernel.org/stable/c/d179a868dd755b0cfcf7582e00943d702b9943b8. For systems unable to immediately patch, disable RxGK support by rebuilding the kernel without CONFIG_AF_RXRPC_RXGK or disable AFS entirely if not required (unload kafs module, set CONFIG_AFS_FS=n), which eliminates the vulnerable code path entirely but breaks AFS functionality for legitimate users. Restrict unprivileged access to add_key() syscall via kernel.unprivileged_userns_clone=0 and user namespace restrictions, though this may impact container runtimes and causes compatibility issues with applications relying on keyring operations. Monitor for unusual add_key() activity with large token sizes via auditd rules (auditctl -a always,exit -F arch=b64 -S add_key -F a2>=1000000), which adds logging overhead but provides detection capability. No configuration-based workaround exists that preserves full RxGK functionality while mitigating the vulnerability.

Same weakness CWE-125 – Out-of-bounds Read

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Vendor StatusVendor

SUSE

Severity: High
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise High Availability Extension 15 SP7 Fixed
SUSE Linux Enterprise High Availability Extension 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed

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EUVD-2026-25534 vulnerability details – vuln.today
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