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CVE-2026-89649
ceph: bound xattr value length in __build_xattrs()
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem fs/ceph. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89649 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
__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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/ceph/xattr.c
- What this is
- CEPH DISTRIBUTED FILE SYSTEM CLIENT (CEPH)MAINTAINERS section matched on fs/ceph/ · ceph-devel@vger.kernel.org · Supported
- Kernel module
- ceph
Check it on the machine
grep -w CONFIG_CEPH_FS /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w cephPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_CEPH_FS
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 9.1 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.68%, higher than 51.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/ceph
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.34 | 5.10.270 | 848b80ca6b41 |
| 2.6.34 | 5.15.221 | 01e3f19c301d |
| 2.6.34 | 6.1.188 | cb0cd79ae804 |
| 2.6.34 | 6.6.157 | 61f085cb8976 |
| 2.6.34 | 6.12.109 | 38be2f3c41ec |
| 2.6.34 | 6.18.50 | 1dd356310b16 |
| 2.6.34 | 7.2.4 | b12b3320c81f |
| 2.6.34 | 7.3 | 68d541754d6c |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- The MDS-supplied xattr blob is delivered over the kernel Ceph messenger TCP session in inode replies (parse_reply_info_in → ceph_fill_inode) and CEPH_MSG_CLIENT_CAPS (handle_cap_grant), so a malicious or compromised MDS reaches __build_xattrs() with network protocol data.
- AC:LAttack complexity, low
- The attacker fully controls the last attribute's 32-bit value length in the xattr blob; setting it larger than the remaining kvmalloc'd wire bytes reliably records an oversized val_len with no race, special memory layout, or rare kernel config.
- PR:NPrivileges required, none
- Exploitation requires only the ability to send crafted MDS replies or cap grants as the remote cluster peer on an established session; no local account, capability, or user-namespace privilege on the victim host is needed.
- UI:NUser interaction, none
- Once CephFS is mounted, MDS replies and cap grants are processed automatically, and ceph_get_acl()/__ceph_getxattr() run on ordinary inode permission checks and xattr queries without a further victim mount or click at exploit time.
- S:UScope, unchanged
- The out-of-bounds heap read, userspace disclosure, and possible oops remain inside the client kernel's own security authority and do not cross a VM, IOMMU, or other distinct trust boundary.
- C:HConfidentiality impact, high
- __set_xattr() stores the oversized length and getxattr memcpy()s that many bytes from the undersized blob into a user buffer (up to XATTR_SIZE_MAX), disclosing adjacent kernel heap including pointers; the in-kernel ACL path can copy still larger extents.
- I:NIntegrity impact, none
- The bug is an out-of-bounds read into a destination buffer sized from the claimed length (VFS kvzalloc or ceph_get_acl kzalloc); it does not provide an attacker-selected write into kernel memory.
- A:HAvailability impact, high
- An oversized value length that extends into unmapped kernel addresses faults the in-kernel memcpy in __ceph_getxattr() or ceph_get_acl(), causing a kernel oops or panic the MDS can trigger repeatedly.