How severe is CVE-2026-80557?

CVE-2026-80557 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-80557?

CVE-2026-80557 affects the following packages: Kernel (Linux). Ecosystems affected: Linux.

How do I fix CVE-2026-80557?

Update Kernel to 5.10.267 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-80557 is resolved across your whole dependency graph.

How do I detect CVE-2026-80557 in my Linux dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2026-80557 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-80557?

O3 pinpoints whether CVE-2026-80557 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2026-80557 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-80557 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-80557?

CVE-2026-80557 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 31th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

When was CVE-2026-80557 published, and has it been updated?

CVE-2026-80557 was published on August 26, 2026 and was last updated on August 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐧

🐧 Linux

Not in CISA KEV

CRITICAL severity

CVE-2026-80557

CRITICAL

CVE-2026-80557 is a critical-severity (CVSS 9.8) vulnerability in Kernel. O3 Security confirms whether CVE-2026-80557 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

libceph: fix OOB read in decode_watchers() via missing bounds check

Published

Aug 26, 2026

Updated

Aug 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Aug 27, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs31th percentile — riskier than 31% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

How urgent is this, really

CVE-2026-80557 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.

Where this sits among everything scored

Of 365,433 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.

Real-World Exposure

1 pkg affected

🐧Kernel

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.

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 ]

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐧Linux	`Kernel`	≥ 4.9.0&&< 5.10.267	5.10.267

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update Kernel to 5.10.267 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-80557 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-80557 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-80557. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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 pre

O3 Security · Impact-Aware SCA

Is CVE-2026-80557 in your dependencies?

O3 detects CVE-2026-80557 across Linux dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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