GHSA-mv28-wj57-f57g: YesWiki Vulnerable to Unauthenticated ActivityPub Signature-Verification Bypass via `!openssl_verify(...)` accepting `int(-1)`

Summary HttpSignatureService::verifySignature() checks the result of PHP's openssl_verify() with a loose boolean negation - if (!openssl_verify(...)) { throw ... }. PHP's openssl_verify has four possible return values: | return | meaning | !return | | ------ | ------------------------------------------------ | --------- | | 1 | signature is valid | false | | 0 | signature is invalid | true ✓ | | -1 | the verify call itself failed (internal error) | false ❌ | | false| input rejected by PHP's argument validation | true ✓ | The -1 row is the bypass: PHP's truthiness rules make -1 a truthy value, so !(-1) === false, the throw is skipped, and the controller proceeds to processActivity(). Any condition that makes OpenSSL's EVP_VerifyFinal() return -1 triggers the bypass. The two practical paths to -1 we are aware of: 1. DSA / EC public key with an RSA-only algorithm. openssl_verify(..., $dsaKey, "RSA-SHA256") returns int(-1) on PHP 8.3 + OpenSSL 3.x. This is the path the PoC uses; it works against an unmodified php:8.3-apache lab and against any deployment using the runtime stack YesWiki's own docker image ships. 2. Older PHP + older OpenSSL where any unrecognised digest name returned -1 rather than false. The reporting research mentions this path; on current stacks false is returned instead and the throw fires correctly. The DSA path replaces it. The reachable consequence is the same in both cases - the controller silently treats a failed verification as success and processes the attacker's payload. Details Affected component - File: tools/bazar/services/HttpSignatureService.php - Method: HttpSignatureService::verifySignature(Request $request) - Sink: line 130 // tools/bazar/services/HttpSignatureService.php (v4.6.5 = origin/doryphore-dev HEAD) public function verifySignature(Request $request) { ... // [Signature parse, // outbound key fetch — see the SSRF advisory] $actorPublicKey = openssl_get_publickey($actor['publicKey']['publicKeyPem']); ... if (!openssl_ver