CVE-2026-50630: Apache CXF CRLF Injection Vulnerability

CVE-2026-50630 Overview

CVE-2026-50630 is a Carriage Return Line Feed (CRLF) injection vulnerability in the Apache CXF OAuth2 AuthorizationUtils class. The flaw allows attackers to inject arbitrary HTTP headers or split HTTP responses when they can influence the realm parameter used to build the WWW-Authenticate response header. The class concatenates the realm value into the header without stripping CR (\r) or LF (\n) characters. Apache has released fixed versions 4.2.2 and 4.1.7. The issue is classified under CWE-113 (Improper Neutralization of CRLF Sequences in HTTP Headers).

Critical Impact
Attackers who control the realm value can inject HTTP headers, perform HTTP response splitting, and enable downstream attacks such as cache poisoning or cross-site scripting.

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 OAuth2 AuthorizationUtils class to build WWW-Authenticate headers

Discovery Timeline

2026-06-12 - CVE-2026-50630 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-50630

Vulnerability Analysis

The vulnerability resides in the OAuth2 AuthorizationUtils class within Apache CXF. When the framework constructs a WWW-Authenticate response header to challenge a client, it concatenates the realm parameter directly into the header value. The concatenation routine does not sanitize, encode, or reject CR (\r, 0x0D) and LF (\n, 0x0A) bytes.

HTTP headers are delimited by \r\n sequences. When attacker-controlled CRLF bytes pass into a header value, the resulting response can contain attacker-defined headers or a separate response body. This category of flaw is commonly called HTTP response splitting.

The impact depends on whether downstream components, proxies, or caches honor the injected content. Successful exploitation can support cross-site scripting, session fixation through forged Set-Cookie headers, or web cache poisoning that affects other users of a shared cache.

Root Cause

The root cause is missing input neutralization in the realm argument flow within AuthorizationUtils. The class trusts the caller-supplied realm string and emits it verbatim into the WWW-Authenticate header. No validation rejects control characters, and no encoding converts them into safe representations.

Attack Vector

The attack vector is network based and requires no authentication or user interaction. Exploitation requires that the attacker influence the realm value used by the application. This typically occurs when developers populate the realm from request parameters, host headers, tenant identifiers, or other untrusted inputs. The attacker submits a request containing CRLF sequences followed by crafted header lines or a complete response body in the realm input.

No verified public exploit code is available. Refer to the Apache mailing list advisory and the Openwall OSS-Security update for vendor details.

Detection Methods for CVE-2026-50630

Indicators of Compromise

HTTP requests containing raw %0d%0a, \r\n, or URL-encoded CRLF sequences in parameters that map to the OAuth2 realm value.
Outbound HTTP responses with unexpected duplicate headers, multiple HTTP/1.1 status lines, or unauthorized Set-Cookie entries.
Web Application Firewall (WAF) or proxy logs showing oversized or multi-line WWW-Authenticate header values.

Detection Strategies

Inspect application and proxy logs for OAuth2 endpoints emitting WWW-Authenticate headers that contain CR or LF characters.
Run software composition analysis to identify Apache CXF versions below 4.2.2 or 4.1.7 in dependency manifests such as pom.xml and build.gradle.
Replay traffic through fuzzing tools that submit CRLF payloads against OAuth2 authorization endpoints and observe response header structure.

Monitoring Recommendations

Enable verbose HTTP response logging on reverse proxies in front of Apache CXF services to capture anomalous header patterns.
Alert on responses where the WWW-Authenticate header length exceeds an established baseline or contains control characters.
Correlate OAuth2 401 responses with downstream cache behavior to detect potential cache poisoning attempts.

How to Mitigate CVE-2026-50630

Immediate Actions Required

Upgrade Apache CXF to version 4.2.2 or 4.1.7 across all affected services.
Audit application code that passes user-controlled input into the OAuth2 realm parameter and remove direct user influence where possible.
Deploy WAF rules that reject HTTP request parameters containing %0d, %0a, or raw CRLF byte sequences targeting OAuth2 endpoints.

Patch Information

Apache has released fixed builds in Apache CXF 4.2.2 and 4.1.7. The patches sanitize CR and LF characters before concatenating the realm value into the WWW-Authenticate header. Patch details are published on the Apache mailing list thread.

Workarounds

Hardcode the realm value to a static, trusted string rather than deriving it from request data.
Implement a servlet filter or interceptor that strips \r and \n from any value placed into outbound response headers.
Place a reverse proxy in front of the application that normalizes response headers and rejects malformed values.

bash

# Maven dependency update example
mvn versions:set-property -Dproperty=cxf.version -DnewVersion=4.2.2
mvn versions:set-property -Dproperty=cxf.version -DnewVersion=4.1.7