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

[Colm O hEigeartaigh <coheigea () apache org>]

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) before 4.1.7

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, which fixes this issue.

Credit:

Guanping Zhang reported this vulnerability. (finder)

References:

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