CVE-2025-48865: Fabio allows HTTP clients to manipulate custom headers it adds

Vulnerability summary

CVE-2025-48865 is a critical (CVSS 9.1) vulnerability in fabiolb fabio. EPSS estimates a 0.47% chance of exploitation in the next 30 days, higher than 40.4% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 30-05-2025
   PublishedVulnerability first disclosed.
2. 30-05-2025
   Last modifiedVulnerability information updated.

Description

Fabio is an HTTP(S) and TCP router for deploying applications managed by consul. Prior to version 1.6.6, Fabio allows clients to remove X-Forwarded headers (except X-Forwarded-For) due to a vulnerability in how it processes hop-by-hop headers. Fabio adds HTTP headers like X-Forwarded-Host and X-Forwarded-Port when routing requests to backend applications. Since the receiving application should trust these headers, allowing HTTP clients to remove or modify them creates potential security vulnerabilities. Some of these custom headers can be removed and, in certain cases, manipulated. The attack relies on the behavior that headers can be defined as hop-by-hop via the HTTP Connection header. This issue has been patched in version 1.6.6.

• CWE-345Insufficient Verification of Data AuthenticityThe product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
• CWE-348Use of Less Trusted SourceThe product has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack.