Look up another CVE · open CVE-2026-80557 in the interactive tracker
CVE-2026-80557
libceph: fix OOB read in decode_watchers() via missing bounds check
Published 2026-08-26 (2 months ago) by the Linux kernel CNA. Subsystem net/ceph. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-80557 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6477-1 · 2026-08-29 · text | 6.12.107-1 | Update the kernel and reboot. DSA-6477-1 shipped the fix on 2026-08-29, in 6.12.107-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
ceph_start_decoding() validates that struct_len bytes remain in the buffer after the encoding header, but accepts struct_len=0 as valid: ceph_decode_need(p, end, 0, bad) always passes. When a malicious or compromised OSD sends an obj_list_watch_response_t reply with struct_len=0, ceph_start_decoding() returns success with p == end, leaving zero bytes guaranteed for subsequent reads. The immediately following ceph_decode_32(p) in decode_watchers() has no preceding bounds check. With p == end this is a 4-byte read past the validated buffer boundary. The garbage value is then passed directly to kzalloc_objs() as the watcher count. The sibling function decode_watcher() already uses the safe variants (ceph_decode_copy_safe, ceph_decode_64_safe, ceph_decode_skip_32) after its own ceph_start_decoding() call. decode_watchers() is the only site that uses the bare variant, confirming an oversight. Fix by replacing ceph_decode_32(p) with ceph_decode_32_safe(p, end, *num_watchers, bad), consistent with the established pattern. Attacker model: a malicious or compromised OSD in a multi-tenant Ceph deployment (e.g. cloud) can trigger this against any kernel client that calls CEPH_OSD_OP_LIST_WATCHERS, without any further privileges beyond OSD session establishment. [ idryomov: trim changelog ]
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.
net/ceph/osd_client.c
- What this is
- CEPH COMMON CODE (LIBCEPH)MAINTAINERS section matched on net/ceph/ · ceph-devel@vger.kernel.org · Supported
- Kernel module
- libceph
Check it on the machine
grep -w CONFIG_CEPH_LIB /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 libcephPrints 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_LIB
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
- 2026-08-26 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.53%, higher than 43.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/ceph
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.9 | 5.10.267 | 85479b7d65b4 |
| 4.9 | 5.15.218 | 1c824e7c75bb |
| 4.9 | 6.1.185 | f161be39201e |
| 4.9 | 6.6.154 | eab3eeb68bfc |
| 4.9 | 6.12.106 | c59219a6b62d |
| 4.9 | 6.18.47 | cb8246e5846d |
| 4.9 | 7.1.10 | 7130d94846da |
| 4.9 | 7.2 | 00ead17c7de1 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6477-1 | 2026-08-29 | trixie 6.12.107-1 | 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 bug is triggered when libceph decodes a crafted MOSDOpReply for CEPH_OSD_OP_LIST_WATCHERS received over the Ceph messenger TCP session from a compromised or malicious OSD; exploitation requires no local syscall, ioctl, or device access on the victim.
- AC:LAttack complexity, low
- A malicious OSD fully controls the reply encoding and can set struct_len=0 with a chosen outdata_len so ceph_start_decoding() leaves p at end and the following ceph_decode_32() deterministically reads attacker-chosen bytes as num_watchers without races or victim-specific memory layout.
- PR:NPrivileges required, none
- The attacker acts as the remote Ceph OSD peer and needs no account, capabilities, or privileges on the victim Linux host; any kernel RBD client connected to a multi-tenant or attacker-controlled cluster is exposed when exclusive-lock recovery issues LIST_WATCHERS.
- UI:NUser interaction, none
- Once an RBD image with exclusive-lock is mapped, ceph_osdc_list_watchers() is invoked automatically during rbd_try_lock() lock-contention recovery; no additional victim user or administrator action is required at exploit time beyond the existing client session.
- S:UScope, unchanged
- The out-of-bounds read, attacker-sized heap allocation, and any resulting kernel memory corruption all occur within the victim host kernel Ceph client; the flaw does not cross VM, container, or IOMMU security boundaries.
- C:HConfidentiality impact, high
- The missing bounds check causes a 4-byte out-of-bounds kernel memory read via ceph_decode_32() when p equals end; per kernel guidance any out-of-bounds read is rated High, and the attacker can place controlled bytes immediately past the validated boundary via outdata_len.
- I:HIntegrity impact, high
- The out-of-bounds or attacker-supplied num_watchers value is passed directly to kzalloc_objs(), giving the remote peer control over kernel heap allocation size and subsequent decode_watchers() processing of watcher structures in the RBD exclusive-lock path.
- A:HAvailability impact, high
- The slab out-of-bounds read can trigger KASAN faults or kernel oops on instrumented builds, and a large attacker-chosen num_watchers can cause ENOMEM/OOM or stall the RBD lock worker during repeated decode_watcher() attempts, producing severe repeatable availability loss.