fix(encryption): read alg/enc exclusively from protected header in JWEDecrypter#658
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rossaddison wants to merge 1 commit into
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fix(encryption): read alg/enc exclusively from protected header in JWEDecrypter#658rossaddison wants to merge 1 commit into
rossaddison wants to merge 1 commit into
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…EDecrypter RFC 7516 §4.1.1 (alg) and §4.1.2 (enc) require both parameters to be integrity-protected. The previous implementation passed the merged $completeHeader (sharedProtectedHeader + sharedHeader + recipientHeader) to getKeyEncryptionAlgorithm() and getContentEncryptionAlgorithm(). Because array_merge() exhibits last-wins behaviour, an attacker could override alg or enc by placing a different value in an unprotected header field, creating a TOCTOU split between HeaderCheckerManager validation and actual decryption. Fix: extract alg/enc exclusively from getSharedProtectedHeader(). The merged $completeHeader is still forwarded to decryptCEK() because ECDH parameters (epk, apu, apv) may legitimately reside in per-recipient unprotected headers. Also adds is_string() guards in both getter methods so a malformed non-string header value cannot reach the AlgorithmManager. Note: JWSVerifier::getAlgorithm() already reads alg from getProtectedHeader() only and is not affected. Fixes web-token#114
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Summary
JWEDecrypter::decryptRecipientKey()builds$completeHeaderby merging the shared protected header, the shared unprotected header, and the per-recipient unprotected header viaarray_merge(). Becausearray_merge()exhibits last-wins behaviour for duplicate string keys, an attacker can override the integrity-protectedalgorencparameters by placing different values in an unprotected header field.This creates a TOCTOU split:
HeaderCheckerManagervalidatesalg/encfrom the protected headergetKeyEncryptionAlgorithm()/getContentEncryptionAlgorithm()previously resolved the algorithm from the merged header where unprotected values winRelated advisory: #114
What this PR does NOT change
JWSVerifier::getAlgorithm()already readsalgexclusively fromgetProtectedHeader()and is not affected.Fix
Pass
$jwe->getSharedProtectedHeader()— the integrity-protected portion — to bothgetKeyEncryptionAlgorithm()andgetContentEncryptionAlgorithm()instead of the merged$completeHeader.The merged
$completeHeaderis still forwarded todecryptCEK()unchanged, because ECDH-ES parameters (epk,apu,apv) may legitimately reside in per-recipient unprotected headers per RFC 7516 §4.6.is_string()guards are added in both getter methods so a malformed non-string header value cannot reach theAlgorithmManager.RFC references
algMUST be integrity-protectedencMUST be integrity-protectedTesting
Please run the existing JWE test suite. A targeted regression test demonstrating the override scenario would be a welcome addition from the maintainers.