CVE-2026-50629: Apache CXF Log Injection Vulnerability

CVE-2026-50629 Overview

CVE-2026-50629 is a log injection vulnerability in Apache CXF. The clientId parameter from incoming HTTP requests flows directly into OAuth2 server log warning messages without sanitization of control characters. Attackers can inject arbitrary content, including forged log entries, into server log files. The flaw is classified under CWE-93: Improper Neutralization of CRLF Sequences. Apache has released fixed versions 4.2.2 and 4.1.7. The vulnerability is exploitable remotely without authentication or user interaction, though it impacts log integrity rather than confidentiality or availability.

Critical Impact
Remote unauthenticated attackers can forge log entries in Apache CXF OAuth2 server logs, undermining audit trails and complicating incident response.

Affected Products

Apache CXF versions prior to 4.2.2 (4.2.x branch)
Apache CXF versions prior to 4.1.7 (4.1.x branch)
Applications using the Apache CXF OAuth2 server component

Discovery Timeline

2026-06-12 - CVE-2026-50629 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-50629

Vulnerability Analysis

The vulnerability resides in the Apache CXF OAuth2 server component. When the server processes an HTTP request containing a clientId parameter, it concatenates that parameter value directly into warning-level log messages. The implementation does not strip or escape control characters such as carriage return (\r) or line feed (\n).

An attacker submits a clientId value containing CRLF sequences followed by arbitrary text. The logging framework writes the value as-is, producing additional lines that appear to be legitimate log entries. This corrupts the log stream and can mislead analysts reviewing OAuth2 authentication activity.

The impact is limited to log integrity. The flaw does not directly expose data or crash the service, but it weakens forensic investigation and can mask malicious activity by drowning real events in fabricated entries.

Root Cause

The root cause is missing output neutralization for log files [CWE-93]. The OAuth2 server warning logger treats untrusted HTTP input as a safe string. No filter strips control characters before the clientId value is appended to the log message template.

Attack Vector

The attack vector is network-based and requires no authentication. An attacker sends an HTTP request to an OAuth2 endpoint exposed by the Apache CXF server. The clientId query parameter or form field carries a payload containing CRLF sequences and forged log content. When the server logs a warning for that request, the injected lines are written verbatim into the log file or downstream log aggregator. Refer to the Apache Security Mailing List Thread for the upstream advisory.

No verified public proof-of-concept code is available for this issue. The vulnerability mechanism is described in the Openwall OSS Security Discussion.

Detection Methods for CVE-2026-50629

Indicators of Compromise

Log entries containing unexpected line breaks, control characters, or duplicated timestamps within OAuth2 warning messages.
Forged log lines that mimic the format of legitimate clientId warnings but appear out of sequence.
HTTP requests to OAuth2 endpoints with clientId parameter values containing URL-encoded %0d, %0a, or raw CRLF bytes.

Detection Strategies

Inspect OAuth2 server access logs for clientId parameter values containing encoded or literal control characters.
Compare structured log fields with raw log file output to identify entries where clientId content breaks the expected line format.
Apply web application firewall rules that flag CRLF sequences in OAuth2 request parameters.

Monitoring Recommendations

Forward Apache CXF logs to a centralized SIEM and parse with strict schemas that reject malformed entries.
Alert on OAuth2 warning messages whose clientId field length or character set deviates from expected client identifier patterns.
Track the volume of OAuth2 warning events per source IP to detect bulk log poisoning attempts.

How to Mitigate CVE-2026-50629

Immediate Actions Required

Upgrade Apache CXF to version 4.2.2 if running the 4.2.x branch.
Upgrade Apache CXF to version 4.1.7 if running the 4.1.x branch.
Audit existing OAuth2 logs for injected entries dated before the upgrade and preserve original files for forensic review.

Patch Information

The Apache CXF project addressed the issue in releases 4.2.2 and 4.1.7. Both releases sanitize control characters in the clientId value before it is written to log messages. Patch details are published in the Apache Security Mailing List Thread.

Workarounds

Place a reverse proxy or WAF in front of the OAuth2 endpoint and reject requests whose clientId parameter contains CRLF or other control characters.
Configure the logging framework to encode or strip non-printable characters before writing to disk.
Restrict access to OAuth2 endpoints to known client networks where feasible until the upgrade is completed.

bash

# Example WAF rule (ModSecurity) to block CRLF in clientId parameter
SecRule ARGS:clientId "@rx [\r\n]" \
    "id:1050629,phase:2,deny,status:400,\
    msg:'CVE-2026-50629: CRLF injection attempt in OAuth2 clientId'"