PHP JWT Library: RSA1_5 (RSAES-PKCS1-v1_5) decryption lacks implicit rejection, exposing a Bleichenbacher/Marvin padding oracle
Impact
RSACrypt::decryptWithRSA15() (used by the RSA1_5 key-encryption algorithm) implements RSAES-PKCS1-v1_5 decryption by inspecting the padding after RSADP and throwing InvalidArgumentException as soon as the padding is malformed. It does not implement the implicit-rejection countermeasure required by RFC 3447 §7.2.2 / RFC 8017 §7.1.2 (return a deterministic pseudo-random value of the expected length on padding failure and let the downstream step fail uniformly).
From a JWE caller this yields a Bleichenbacher/Marvin padding oracle: an attacker submitting adaptively crafted encrypted_key values can distinguish (a) padding rejected, (b) padding valid but wrong CEK length, and (c) padding valid and full AEAD executed — even though JWEDecrypter returns the same false in all cases — because each path performs a measurably different amount of work, amplifiable by enlarging the ciphertext (CWE-208 timing side channel). Enough adaptive queries can recover the wrapped CEK.
Affected configurations
Applications that register RSA1_5 in their decryption AlgorithmManager and hold an RSA private key.
Patches
PKCS#1 v1.5 decryption now performs implicit rejection: on invalid padding (or unexpected recovered length) it returns a random CEK of the expected size selected in constant time, so the full content-decryption (AEAD) step always runs and fails uniformly, removing the observable difference between padding-valid and padding-invalid ciphertexts. Users are still strongly encouraged to migrate to RSA-OAEP.
Workarounds
Prefer RSA-OAEP/RSA-OAEP-256; do not enable RSA1_5 for untrusted tokens.
References
- RFC 3447 §7.2.2 / RFC 8017 §7.1.2
- Bleichenbacher (1998); Marvin attack
- CWE-208: Observable Timing Discrepancy
Résolution
Un correctif a été préparé sur une branche dédiée basée sur 3.4.x, avec des tests anti-régression dédiés (fork privé temporaire de cette advisory, PR #1).
RSA1_5 — déchiffrement PKCS#1 v1.5 avec implicit rejection en temps constant (RFC 3447 §7.2.2) : un padding invalide n'est plus distinguable d'un padding valide, neutralisant l'oracle Bleichenbacher.
Validation : php -l OK, PHPUnit vert, aucune nouvelle erreur PHPStan introduite (différentiel nul vs 3.4.x), aucun commentaire ajouté dans le code source. Après merge, cascade prévue 3.4.x → 4.0.x → 4.1.x.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | web-token/jwt-library | < 3.4.10, >= 4.0.0, < 4.0.7, >= 4.1.0, < 4.1.7 | 3.4.10, 4.0.7, 4.1.7 |
References
- CVSS vector
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-208, CWE-385- Platform
- Composer
- Package
web-token/jwt-library- Disclosed
- 18.06.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-5739-39v2-5754 - CC BY 4.0
Vulnerability history: web-token/jwt-library
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 4
- First → latest
- 06.2026 06.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
- Medium 2
Disclosures per year
- 2026: 4
-
PHP JWT Library: RSA1_5 (RSAES-PKCS1-v1_5) decryption lacks implicit rejection, exposing a Bleichenbacher/Marvin padding oracle this entry
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