CVE-2026-80557: Linux kernel · libceph: fix OOB read in decode_watchers() via missing bounds check
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 9.8 Critical.
Data as of 27 Oct 2026, 05:11 UTC
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 44% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 26 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-gkepkg:deb/ubuntu/linux-gke?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A fix for this vulnerability has been implemented in the Linux kernel by replacing the unsafe decode call with a safe variant that performs proper bounds checking. Users should apply the official kernel updates that include this patch. Since this is a kernel-level vulnerability, updating to a patched kernel version is the recommended remediation. No additional mitigations are specified or required beyond applying the official fix.
Description
In the Linux kernel, the following vulnerability has been resolved: libceph: fix OOB read in decode_watchers() via missing bounds check 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 ]
References
- nvd.nist.gov/vuln/detail/CVE-2026-80557 (opens in a new tab)
- git.kernel.org/stable/c/00ead17c7de137a692edee59f2772e6af687e8eb (opens in a new tab)
- git.kernel.org/stable/c/7130d94846dadbb97b6b7f4d78a3a7bba6e3daa1 (opens in a new tab)
- ubuntu.com/security/CVE-2026-80557 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-80557 (opens in a new tab)
- git.kernel.org/stable/c/1c824e7c75bb4adf19553dd4ea944a5d83096be8 (opens in a new tab)
- git.kernel.org/stable/c/cb8246e5846dbbe34930903a90c7a90dd8e5910b (opens in a new tab)
- git.kernel.org/stable/c/f161be39201eb5f9b1f58fb8f90b8a9cd3931eb6 (opens in a new tab)
- git.kernel.org/stable/c/c59219a6b62d74936963983e5815524c3de8dd79 (opens in a new tab)
- git.kernel.org/stable/c/eab3eeb68bfc639d74f27256f05546af5c4f787d (opens in a new tab)
- git.kernel.org/stable/c/85479b7d65b4ebcb07fbbe57230976793974ab4a (opens in a new tab)