potatosalad jose 1.10.0/1.11.12 Curve25519 jose_jwa_x25519:scalarmult timing discrepancy

Summaryinfo

A vulnerability was found in potatosalad jose 1.10.0/1.11.12 and classified as problematic. Affected is the function jose_jwa_x25519:scalarmult of the component Curve25519. The manipulation results in timing discrepancy. This vulnerability is reported as CVE-2026-65630. The attack can be launched remotely. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in potatosalad jose 1.10.0/1.11.12. Affected is the function jose_jwa_x25519:scalarmult of the component Curve25519. The manipulation with an unknown input leads to a timing discrepancy vulnerability. CWE is classifying the issue as CWE-208. Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not. This is going to have an impact on confidentiality. CVE summarizes:

Observable Timing Discrepancy vulnerability in potatosalad jose allows recovery of a long-term X25519 private key through a timing side channel in the pure-Erlang Curve25519 fallback. The pure-Erlang X25519 implementation performs scalar multiplication over the secret private key using a recursive Montgomery ladder (jose_jwa_x25519:curve25519/2) whose clauses branch on individual bits of the clamped private scalar, and whose per-step operations (jose_jwa_x25519:montgomery_add/3 and jose_jwa_x25519:montgomery_double/1) and field inversion are built from value-dependent Erlang bignum arithmetic (multiplication, remainder, and modular exponentiation). Although the ladder is operation-count balanced and fixed at 254 steps, the concrete integer values processed at each step, and therefore the running time, depend on the secret scalar. The execution time of the public entry points jose_jwa_x25519:scalarmult/2, jose_jwa_x25519:x25519/2, jose_jwa_x25519:x25519_base/1, and jose_jwa_x25519:sk_to_pk/1 is thus a function of the private key. This path is reachable from the public API, most notably when a service decrypts attacker-supplied ECDH-ES (JWE) messages with a long-term X25519 key (for example through JOSE.JWK.box_decrypt_ecdh_es/2, which reaches jose_jwa_curve25519:x25519_shared_secret/2 and the ladder). An attacker who can submit ciphertexts and measure decryption timing can, in principle, recover the private key bit by bit, defeating the resistance X25519 was designed to provide. Recovery of the key compromises the confidentiality and authenticity of all data protected by it. This issue affects jose: from 1.10.0 before 1.11.13.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-65630 since 07/22/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1592.

Upgrading to version 1.11.13 eliminates this vulnerability.

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Productinfo

Vendor

• potatosalad

Name

• jose

Version

• 1.10.0
• 1.11.12

CPE 2.3info

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CPE 2.2info

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