CVE-2026-39944

Aliases:DEBIAN-CVE-2026-39944UBUNTU-CVE-2026-39944
Advisory lineage Upstream: 0 Downstream: 1
Downstream
MGASA-2026-0389
Awaiting Analysis
Published: 27 Aug 2026, 20:47
Last modified:01 Sept 2026, 03:56

Vulnerability Summary

Overall Risk (default)
medium
35/100
CVSS Score
8.8 HIGH
v3.1 (cve.org)
EPSS Score
0.17% LOW
0% probability 0.00%
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

27 Aug 2026, 20:47
Published
Vulnerability first disclosed
01 Sept 2026, 03:56
Last Modified
Vulnerability information updated

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.

CVSS Metrics

  • v3.1•HIGH•Score: 8.8CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS Trends

Current EPSS score: 0.17%• Percentile: 7%

Techniques & Countermeasures

  • CWE-327•Use of a Broken or Risky Cryptographic Algorithm

    The product uses a broken or risky cryptographic algorithm or protocol.

Affected Systems

  • ceph•ceph

    ≥ 19.0.0, < 19.2.6 | ≥ 20.0.0, < 20.2.4

  • debian•ceph

    all | all | all | all | < 20.2.4+ds-1

  • ubuntu•ceph

    all | all | all | all

References (7)