Skip to content

fix: stop CSP allow-lists triggering challenge detection (#264) #266

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
ankitranjan7 wants to merge 2 commits into
base: main
Choose a base branch
from
+35 −2
Open

fix: stop CSP allow-lists triggering challenge detection (#264) #266

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
b8bd787
fix: stop CSP allow-lists triggering challenge detection (#264)
ankitranjan7 Aug 10, 2026
34ffd00
fix: keep decisive challenge headers while ignoring CSP allow-lists
ankitranjan7 Aug 11, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
19 changes: 19 additions & 0 deletions src/fetch/classify.test.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,25 @@ describe('fetch classification', () => {
it('recognizes explicit challenges but not bare forbidden responses', () => {
expect(isChallengeResponse(403, { server: 'cloudflare' }, 'Just a moment...')).toBe(true);
expect(isChallengeResponse(403, {}, 'forbidden')).toBe(false);
expect(isChallengeResponse(403, { server: 'cloudflare' }, 'forbidden')).toBe(true);
});
it('ignores third-party allow-lists in CSP and friends', () => {
const csp = "default-src 'self'; script-src https://www.google.com/recaptcha/ https://cdnjs.cloudflare.com/";
expect(isChallengeResponse(200, { 'content-security-policy': csp }, '<html>Hacker News</html>')).toBe(false);
expect(isChallengeResponse(403, { 'content-security-policy': csp }, 'forbidden')).toBe(false);
});
it('does not treat a served 200 as a challenge on headers alone', () => {
expect(isChallengeResponse(200, { server: 'cloudflare' }, '<html>real page</html>')).toBe(false);
expect(isChallengeResponse(200, { server: 'cloudflare' }, 'Just a moment...')).toBe(true);
});
it('treats cf-mitigated: challenge as decisive, even on a 200', () => {
expect(isChallengeResponse(200, { 'cf-mitigated': 'challenge' }, '<html>looks fine</html>')).toBe(true);
expect(isChallengeResponse(403, { 'cf-mitigated': 'challenge' }, 'forbidden')).toBe(true);
});
it('reads decisive evidence from the header name, not just its value', () => {
expect(isChallengeResponse(403, { 'cf-chl-out': 'AAAA1111' }, 'forbidden')).toBe(true);
expect(isChallengeResponse(403, { 'x-datadome': 'protected' }, 'forbidden')).toBe(true);
expect(isChallengeResponse(403, { 'x-datadome-cid': 'abc123' }, 'forbidden')).toBe(true);
});
it('recognizes script-heavy app shells', () => expect(isJavaScriptShell('<div id="root"></div><script src="/app.js"></script><script>boot()</script>')).toBe(true));
});
18 changes: 16 additions & 2 deletions src/fetch/classify.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,8 +1,22 @@
const challengeMarkers = /cloudflare|cf-chl|datadome|perimeterx|px-captcha|akamai|captcha|just a moment|verify you are human/i;
// Headers a bot-mitigation product sets *because it challenged this request*. The evidence is in
// the name — values are opaque tokens — so these are decisive on their own, whatever the status.
// https://developers.cloudflare.com/cloudflare-challenges/challenge-types/challenge-pages/detect-response/
const decisiveHeaders = /^(?:cf-chl-[\w-]+|x-datadome[\w-]*)$/i;
// Provider branding: present on every response the provider proxies, challenge or not. It can
// support an already-blocked status but must never turn a served 200 into a challenge.
const weakHeaders = /^(?:server|set-cookie)$/i;
// CSP/report-to/link are allow-lists of third parties (cdnjs.cloudflare.com, google.com/recaptcha)
// and are evidence of nothing — they are in neither list.

export function isChallengeResponse(status: number, headers: Record<string, string>, body: string): boolean {
const evidence = `${Object.entries(headers).map(([key, value]) => `${key}:${value}`).join('\n')}\n${body.slice(0, 20_000)}`;
return challengeMarkers.test(evidence) && (status === 403 || status === 429 || status === 503 || status === 200);
if (status !== 403 && status !== 429 && status !== 503 && status !== 200) return false;
if (challengeMarkers.test(body.slice(0, 20_000))) return true;
const entries = Object.entries(headers).map(([key, value]) => [key.trim().toLowerCase(), value] as const);
if (entries.some(([key, value]) => decisiveHeaders.test(key) || (key === 'cf-mitigated' && /challenge/i.test(value)))) return true;
// A 200 with a real body is a served page; branding alone (server: cloudflare) never proves otherwise.
if (status === 200) return false;
return entries.some(([key, value]) => weakHeaders.test(key) && challengeMarkers.test(value));
}

export function isJavaScriptShell(body: string): boolean {
Expand Down