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HIGH

CVE-2026-39944

CVSS v3

8.8

HIGH

EPSS Score

0.3 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • cephBitnamifrom 19.0.0 · fixed in 19.2.6

Vendor advisories

  • CVE-2026-39944 Red Hat Product Security225 products fixed · 166 known affected

    ceph: ceph: RGW STS session tokens vulnerable to CBC bit-flip attack enabling admin privilege escalation

    ceph-base as a component of Red Hat Ceph Storage 4 · ceph-common as a component of Red Hat Ceph Storage 4 · ceph-fuse as a component of Red Hat Ceph Storage 4

  • RHSA-2026:79243 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: Red Hat Ceph Storage

  • RHSA-2026:79101 Red Hat Product Security221 products fixed

    Red Hat Security Advisory: Red Hat Ceph Storage 8.1 security and bug fix updates

Full record on NVD

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.

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Published
2026-08-28
Last Modified
2026-08-28

Frequently asked questions

What is CVE-2026-39944?

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.

Is CVE-2026-39944 actively exploited?

Active exploitation of CVE-2026-39944 has not been confirmed. Its EPSS score was 0.3% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-39944?

CVE-2026-39944 has a CVSS v3 base score of 8.8 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

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