CVE-2023-25725
📋 TL;DR
CVE-2023-25725 is an HTTP request smuggling vulnerability in HAProxy that allows attackers to bypass access controls by sending specially crafted HTTP headers. The vulnerability occurs because HAProxy accepts empty header field names, which can truncate the header list and make security headers disappear during processing. This affects all HAProxy users running vulnerable versions before the patched releases.
💻 Affected Systems
- HAProxy
📦 What is this software?
Haproxy by Haproxy
Haproxy by Haproxy
Haproxy by Haproxy
Haproxy by Haproxy
Haproxy by Haproxy
Haproxy by Haproxy
⚠️ Risk & Real-World Impact
Worst Case
Complete bypass of authentication, authorization, and security controls leading to unauthorized access to backend systems and sensitive data exposure.
Likely Case
Partial access control bypass allowing attackers to reach restricted endpoints or services that should be protected by HAProxy rules.
If Mitigated
Limited impact if proper defense-in-depth controls exist, such as additional authentication layers at backend services.
🎯 Exploit Status
Exploitation requires sending specially crafted HTTP requests with empty header names. The vulnerability is well-documented and patches are available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.7.3, 2.6.9, 2.5.12, 2.4.22, 2.2.29, or 2.0.31 depending on your branch
Vendor Advisory: https://git.haproxy.org/?p=haproxy-2.7.git;a=commit;h=a0e561ad7f29ed50c473f5a9da664267b60d1112
Restart Required: Yes
Instructions:
1. Identify your HAProxy version. 2. Upgrade to the appropriate patched version for your branch. 3. Restart HAProxy service. 4. Verify the upgrade was successful.
🔧 Temporary Workarounds
HTTP/2 or HTTP/3 Enforcement
linuxForce clients to use HTTP/2 or HTTP/3 where possible, as these protocols have limited impact from this vulnerability.
# Configure HAProxy to prefer HTTP/2/3 in frontend sections
bind :443 ssl crt /etc/ssl/certs/example.pem alpn h2,http/1.1
🧯 If You Can't Patch
- Implement additional authentication and authorization at backend services to create defense-in-depth
- Deploy a WAF (Web Application Firewall) in front of HAProxy to detect and block malicious HTTP requests
🔍 How to Verify
Check if Vulnerable:
Check HAProxy version and compare against vulnerable versions. Test with crafted HTTP requests containing empty header names.Check Version:
haproxy -vVerify Fix Applied:
Verify HAProxy version is patched and test that empty header names are properly rejected.📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP requests with malformed headers
- Access to restricted endpoints without proper authentication logs
- HTTP 400 errors related to header parsing
Network Indicators:
- HTTP requests containing headers with empty names
- Unusual patterns of requests bypassing expected access controls
SIEM Query:
source="haproxy.log" AND (http_request contains "\r\n:\" OR http_header contains empty_field)🔗 References
- https://git.haproxy.org/?p=haproxy-2.7.git%3Ba=commit%3Bh=a0e561ad7f29ed50c473f5a9da664267b60d1112
- https://lists.debian.org/debian-lts-announce/2023/02/msg00012.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FPTJQHKUEU2PQ7RWFUYAFLAD4STEIKHU/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JM5NCIBTHYDTLPY2UNC4HO2VAHHE6CJG/
- https://www.debian.org/security/2023/dsa-5348
- https://www.haproxy.org/
- https://git.haproxy.org/?p=haproxy-2.7.git%3Ba=commit%3Bh=a0e561ad7f29ed50c473f5a9da664267b60d1112
- https://lists.debian.org/debian-lts-announce/2023/02/msg00012.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FPTJQHKUEU2PQ7RWFUYAFLAD4STEIKHU/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JM5NCIBTHYDTLPY2UNC4HO2VAHHE6CJG/
- https://www.debian.org/security/2023/dsa-5348
- https://www.haproxy.org/
