CVE-2024-51501: CRLF injection in Refit's [Header], [HeaderCollection] and [Authorize] attributes

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.6%, percentile 46: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 46% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes Refit (NuGet) < 7.2.22, fixed in 7.2.22. Check your lockfile, including transitive dependencies.

What it is

Refit is an automatic type-safe REST library for .NET Core, Xamarin and .NET The various header-related Refit attributes (Header, HeaderCollection and Authorize) are vulnerable to CRLF injection. The way HTTP headers are added to a request is via the HttpHeaders.TryAddWithoutValidation method. This method does not check for CRLF characters in the header value. This means that any headers added to a refit request are vulnerable to CRLF-injection. In general, CRLF-injection into a HTTP header (when using HTTP/1.1) means that one can inject additional HTTP headers or smuggle whole HTTP requests. If an application using the Refit library passes a user-controllable value through to a header, then that application becomes vulnerable to CRLF-injection. This is not necessarily a security issue for a command line application like the one above, but if such code were present in a web application then it becomes vulnerable to request splitting (as shown in the PoC) and thus Server Side Request Forgery. Strictly speaking this is a potential vulnerability in applications using Refit and not in Refit itself. This issue has been addressed in release versions 7.2.22 and 8.0.0 and all users are advised to upgrade. There are no known workarounds for this vulnerability.

From the GitHub advisory

Summary The various header-related Refit attributes (Header, HeaderCollection and Authorize) are vulnerable to CRLF injection.

Details The way HTTP headers are added to a request is via the HttpHeaders.TryAddWithoutValidation method: This method does not check for CRLF characters in the header value.

This means that any headers added to a refit request are vulnerable to CRLF-injection. In general, CRLF-injection into a HTTP header (when using HTTP/1.1) means that one can inject additional HTTP headers or smuggle whole HTTP requests.

PoC The below example code creates a console app that takes one command line variable (a bearer token) and then makes a request to some status page with the provided token inserted in the "Authorization" header:

This application is now vulnerable to CRLF-injection, and can thus be abused to for example perform request splitting and thus server side request forgery (SSRF):

Weakness type: CWE-93.

Product: Refit (NuGet) · Assigned by: GitHub_M · Published: 2024-11-04

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.56% probability of exploitation activity in the next 30 days; percentile 46.

Timeline

• 2024-11-04 — CVE record published by GitHub_M
• 2024-11-04 — GitHub-reviewed advisory GHSA-3hxg-fxwm-8gf7 published (critical)
• 2024-11-08 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-3hxg-fxwm-8gf7 github.com
2. CVE.org record CVE-2024-51501 cve.org
3. NVD entry CVE-2024-51501 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical NuGet advisories · Today’s Security Digest