CVE-2026-50631: Apache CXF: OAuth2: TOCTOU Race Condition in Refresh Token Processing 

Severity: low 

Affected versions:

- Apache CXF (org.apache.cxf:cxf-rt-rs-security-oauth2) 4.2.0 before 4.2.2
- Apache CXF (org.apache.cxf:cxf-rt-rs-security-oauth2) 4.0.0 before 4.1.7
- Apache CXF (org.apache.cxf:cxf-rt-rs-security-oauth2) before 3.6.12

Description:

A race condition in AbstractOAuthDataProvider allows concurrent requests using the same Refresh Token to bypass single-use semantics and generate multiple valid Access Tokens, when 'recycleRefreshTokens' is set to false. A leaked refresh token can be replayed concurrently by multiple attackers or threads. Users are recommended to upgrade to versions 4.2.2 or 4.1.7 or 3.6.12, which fixes this issue.

Credit:

Guanping Zhang reported this vulnerability. (finder)

References:

https://lists.apache.org/thread/s83t3x4r626o9h8rt0ryr1w7w53l1vv8
https://cxf.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-50631