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PHP JWT Framework: Chacha20Poly1305 key-encryption algorithm discards the Poly1305 authentication tag, performing no authentication on decryption

Moderate severity GitHub Reviewed Published Jun 6, 2026 in web-token/jwt-framework

Package

composer web-token/jwt-experimental (Composer)

Affected versions

<= 4.1.6

Patched versions

None
composer web-token/jwt-library (Composer)
< 3.4.10
>= 4.0.0, < 4.0.7
>= 4.1.0, < 4.1.7
3.4.10
4.0.7
4.1.7

Description

Impact

The experimental Chacha20Poly1305 key-encryption algorithm generates the 16-byte Poly1305 authentication tag during encryptKey() but discards it: the tag is never written to the header and therefore never reaches the wire. On the receiving side, decryptKey() calls openssl_decrypt('chacha20-poly1305', ...) without the tag argument, which makes OpenSSL skip authentication entirely.

As a result the AEAD construction is silently degraded to unauthenticated ChaCha20: a tampered encrypted CEK is accepted, and because ChaCha20 is a stream cipher, a single-byte change in the ciphertext propagates as a single-byte change in the recovered CEK with no integrity check (CWE-353 / CWE-347). An attacker on the token path can manipulate the wrapped key without detection.

Affected configurations

Applications that register Jose\Experimental\KeyEncryption\Chacha20Poly1305 (package web-token/jwt-experimental) as a JWE alg.

Patches

encryptKey() now publishes the Poly1305 tag as the base64url tag header parameter (and asserts it is 16 bytes). decryptKey() requires the tag header, validates its length, and passes it to openssl_decrypt() so the tag is actually verified, in line with RFC 7539 / RFC 8439. Tampering now results in a decryption failure.

Note: this changes the wire format of tokens produced with this experimental algorithm (a tag header is now emitted and required).

Workarounds

Do not use the experimental Chacha20Poly1305 key-encryption algorithm for untrusted input until upgraded.

References

  • RFC 7539 / RFC 8439 (ChaCha20-Poly1305 AEAD)
  • CWE-353: Missing Support for Integrity Check

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).

ChaCha20-Poly1305 — le tag d'authentification Poly1305 est désormais publié dans le header au chiffrement et vérifié au déchiffrement (RFC 7539), rétablissant l'intégrité AEAD.

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.

References

@Spomky Spomky published to web-token/jwt-framework Jun 6, 2026
Published to the GitHub Advisory Database Jun 18, 2026
Reviewed Jun 18, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Adjacent
Attack Complexity High
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity High
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:A/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

EPSS score

Weaknesses

Improper Verification of Cryptographic Signature

The product does not verify, or incorrectly verifies, the cryptographic signature for data. Learn more on MITRE.

Missing Support for Integrity Check

The product uses a transmission protocol that does not include a mechanism for verifying the integrity of the data during transmission, such as a checksum. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-6vvh-pxr4-25r7

Source code

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