Anubis: Policy bypass via client controlled X-Original-URI header

Any HTTP client can bypass Anubis bot protection on the default configuration by adding a single request header. No challenge needs to be solved. Affected versions: v1.22.0 through v1.25.0 (introduced in commit d1d631a, PR #1015) The root cause is in `lib/policy/checker.go`, `PathChecker.Check()`: ```go func (pc *PathChecker) Check(r *http.Request) (bool, error) { originalUrl := r.Header.Get("X-Original-URI") if originalUrl != "" { if pc.regexp.MatchString(originalUrl) { return true, nil } } if pc.regexp.MatchString(r.URL.Path) { return true, nil } return false, nil } ``` The header value comes directly from the client request. The middleware chain never strips it. In reverse proxy mode an attacker fully controls it. The default policy imports `data/common/keep-internet-working.yaml`, which contains path-only ALLOW rules with no other conditions: ```yaml - name: well-known path_regex: ^/\.well-known/.*$ action: ALLOW ``` When `X-Original-URI` matches one of those regexes, the rule fires as ALLOW and the request is forwarded upstream without any challenge or JWT check. # Proof of concept Normal request, gets challenged: ``` curl -s https://anubis.techaro.lol/ | grep -o "<title>.*</title>" ``` Bypass, gets upstream content: ``` curl -s -H "X-Original-URI: /.well-known/x" https://anubis.techaro.lol/ | grep -o "<title>.*</title>" ``` The first command returns the Anubis challenge page title. The second returns the real site title directly, with no cookie set and no challenge issued. Verified live against anubis.techaro.lol. # Suggested fix The fix should probably be to strip the header from incoming client requests in the middleware chain before policy evaluation. In `auth_request` mode the header is set by the proxy after Anubis processes the middleware, so stripping it at ingress does not break that deployment mode.

Source published

2 Oct 2026 18:22:08 UTC

Source modified

7 Oct 2026 17:55:39 UTC

Observed here

24 Oct 2026 13:19:41 UTC

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GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N

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