Vulnerability · Published May 30, 2025 · Assigned by GitHub_M

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

Critical 9.1

In plain English

A critical-severity insufficient verification of data authenticity in fabio from fabiolb. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.1Critical

Exploit odds (30 days)0.5%top 59.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/fabiolb/fabio	1.6.6	GO-2025-3722
Go	github.com/fabiolb/fabio	1.6.6	GHSA-q7p4-7xjv-j3wf

Affected products (as reported)

Vendor	Product	Versions
fabiolb	fabio	< 1.6.6

Weakness: CWE-345, CWE-348 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

References

https://github.com/fabiolb/fabio/security/advisories/GHSA-q7p4-7xjv-j3wf x_refsource_CONFIRM
https://github.com/fabiolb/fabio/commit/fdaf1e966162e9dd3b347ffdd0647b39dc71a1a3 x_refsource_MISC
https://github.com/fabiolb/fabio/releases/tag/v1.6.6 x_refsource_MISC