nosurf is cross-site request forgery (CSRF) protection middleware for Go. A vulnerability in versions prior to 1.2.0 allows an attacker who controls content on the target site, or on a subdomain of the target site (either via XSS, or otherwise) to bypass CSRF checks and issue requests on user's behalf. Due to misuse of the Go `net/http` library, nosurf categorizes all incoming requests as plain-text HTTP requests, in which case the `Referer` header is not checked to have the same origin as the target webpage. If the attacker has control over HTML contents on either the target website (e.g. `example.com`), or on a website hosted on a subdomain of the target (e.g. `attacker.example.com`), they will also be able to manipulate cookies set for the target website. By acquiring the secret CSRF token from the cookie, or overriding the cookie with a new token known to the attacker, `attacker.example.com` is able to craft cross-site requests to `example.com`. A patch for the issue was released in nosurf 1.2.0. In lieu of upgrading to a patched version of nosurf, users may additionally use another HTTP middleware to ensure that a non-safe HTTP request is coming from the same origin (e.g. by requiring a `Sec-Fetch-Site: same-origin` header in the request).
Affected: Go: github.com/justinas/nosurf
### Impact
This vulnerability allows an attacker who controls content on the target site, or on a subdomain of the target site (either via XSS, or otherwise) to bypass Cross-Site Request Forgery checks and issue requests on user's behalf.
### Details
Due to misuse of the Go `net/http` library, nosurf categorizes all incoming requests as plain-text HTTP requests, in which case the `Referer` header is not checked to have the same origin as the target webpage.
If the attacker has control over HTML contents on either the target website (e.g. `example.com`), or on a website hosted on a subdomain of the target (e.g. `attacker.example.com`), they will also be able to manipulate cookies set for the target website. By acquiring the secret CSRF token from the cookie, or overriding the cookie with a new token known to the attacker, `attacker.example.com` is able to craft cross-site requests to `example.com`.
### Patches
A patch for the issue was released in nosurf 1.2.0.
### Workarounds
In lieu of upgrading to a patched version of nosurf, users may additionally use another HTTP middleware to ensure that a non-safe HTTP request is coming from the same origin (e.g. by requiring a `Sec-Fetch-Site: same-origin` header in the request).
### References
https://github.com/advisories/GHSA-rq77-p4h8-4crw https://github.com/justinas/nosurf-cve-2025-46721 https://www.cve.org/CVERecord?id=CVE-2025-46721 https://github.com/justinas/nosurf/releases/tag/v1.2.0
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