CVE-2026-89649
CriticalCVSS 9.1Exploitation Probability (EPSS)
Low risk9th percentile - higher than 9% of all known CVEs
Summary
A vulnerability exists in the Linux kernel's __build_xattrs() function in the Ceph subsystem, which decodes xattr attributes supplied by the MDS server. Missing bounds checking on the last attribute's value length allows a malicious or compromised metadata server to set a length larger than the actual buffer size, leading to an out-of-bounds read. The fix adds the required ceph_decode_need() check, returning -EIO instead of storing the invalid length.
Risk Assessment
A malicious metadata server can disclose adjacent kernel heap bytes to a local user via getxattr(2) on a CephFS file. This constitutes a kernel memory information leak that could be leveraged to bypass protections such as KASLR.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-89649. If updating is not possible, restrict access to untrusted Ceph metadata servers or consider disabling CephFS mounts on affected systems.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: ceph: bound xattr value length in __build_xattrs() __build_xattrs() decodes the MDS-supplied xattr blob one attribute at a time. For each attribute it reads a 32-bit name length, advances past the name bytes, reads a 32-bit value length, records the value pointer, and advances past the value bytes. The two length fields are read with ceph_decode_32_safe(), but the value bytes themselves are advanced over with a bare "p += len" and no ceph_decode_need() check that "len" bytes remain in the blob. For every attribute except the last, the next iteration's ceph_decode_32_safe() on the following name length implicitly verifies that the previous value did not run past the blob end. The final attribute has no successor, so its decoded value length is never checked against the blob bounds. A malicious or compromised metadata server can set the last attribute's value length larger than the bytes actually present in the blob. The blob is a dedicated kvmalloc() allocation sized to the wire length (ceph_buffer_new() in ceph_fill_inode()). __set_xattr() records the oversized length in xattr->val_len verbatim, and a later getxattr(2) runs memcpy(value, xattr->val, xattr->val_len) into a user-supplied buffer, copying bytes past the end of the allocation back to user space. Impact: a malicious metadata server discloses adjacent kernel heap bytes to a local user via getxattr(2) on a CephFS file. Add the missing ceph_decode_need() so an out-of-bounds value length on the final attribute fails the decode and returns -EIO instead of being stored.