CVE-2026-89651

Received Received - Intake

Buffer Overflow in Linux Kernel Ceph Client

Publication date: 2026-09-11

Last updated on: 2026-09-13

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: ceph: bound MDSCapAuth path and fs_name decode in handle_session() handle_session() decodes the MDSCapAuth records carried by a CEPH_SESSION_OPEN message (msg_version >= 6). For each record the match.path and match.fs_name byte strings are read by first decoding a 32-bit length and then copying that many bytes with the bare ceph_decode_copy(). Unlike the surrounding fields, which all use the _safe decode variants, these two copies are not preceded by a ceph_decode_need() bounds check, and the enclosing MDSCapAuth and MDSCapMatch struct_len fields are skipped rather than enforced as an upper bound. A length larger than the bytes remaining in the message front makes ceph_decode_copy() read past the end of the front buffer. The message front is a dedicated allocation (ceph_msg_new2() -> kvmalloc), so the over-read runs off that object. A malicious or compromised MDS can trigger this with the first post-connect message on mount, with no client-side user interaction; under KASAN it is reported as a slab-out-of-bounds read in handle_session(). Impact: a malicious MDS can force the kernel client to read up to 4 GiB past the message front allocation during session setup, crashing the client (out-of-bounds read). Switch both copies to ceph_decode_copy_safe(), which performs the ceph_decode_need() bounds check before the copy and branches to the existing bad label, matching the rest of the decoder and the error path that frees the partially decoded cap_auths array.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-09-11

Last Modified

2026-09-13

Generated

2026-10-02

AI Q&A

2026-09-12

EPSS Evaluated

2026-10-01

NVD

CVE-2026-89651

EUVD

EUVD-2026-76563

Affected Vendors & Products

Vendor	Product	Version / Range
ceph	ceph	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability in the Linux kernel involves a flaw in the ceph filesystem driver where the handle_session() function decodes MDSCapAuth records without proper bounds checking. Specifically, it reads match.path and match.fs_name byte strings by copying data without verifying if the length exceeds the available buffer, leading to a potential out-of-bounds read.

Detection Guidance

This vulnerability is specific to the Linux kernel's Ceph client implementation and requires kernel-level inspection. Detection involves checking kernel logs for slab-out-of-bounds errors during Ceph session setup. Use 'dmesg | grep -i slab' or 'journalctl -k | grep -i slab' to search for such errors. If you suspect exploitation, monitor for crashes in Ceph clients during mount operations.

Impact Analysis

A malicious or compromised MDS (Metadata Server) can exploit this vulnerability to force the kernel client to read past the allocated message buffer during session setup. This can crash the client due to an out-of-bounds read, potentially causing system instability or denial of service.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR or HIPAA as it involves a kernel-level memory read issue in the Linux Ceph client. It could indirectly impact compliance if exploited to crash systems handling sensitive data, potentially leading to data processing interruptions or unauthorized access during session setup.

Mitigation Strategies

Apply the latest Linux kernel patches that fix the ceph: handle_session() bounds check issue. If immediate patching is not possible, restrict access to untrusted MDS servers or disable Ceph client mounts until patched. Monitor vendor advisories for updates to Ceph packages.

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