CVE-2026-4258 affects sjcl versions prior to 1.0.9 and involves improper verification of cryptographic signatures. The vulnerability is caused by the lack of point-on-curve validation in sjcl.ecc.basicKey.publicKey(), which enables attackers to submit crafted off-curve public keys. By doing so and observing the outputs of the ECDH key exchange, attackers can recover the victim's ECDH private key. The dhJavaEc() function exacerbates this issue by returning the raw x-coordinate of the scalar multiplication result without hashing, thus leaking sensitive information directly.

An attacker can recover the victim's ECDH private key, compromising the confidentiality of cryptographic operations relying on this key. This undermines the security guarantees of ECDH key exchanges performed using vulnerable versions of sjcl, potentially allowing decryption of sensitive communications or impersonation.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or patch link is provided at this time. Users should monitor sjcl vendor communications for updates and avoid using vulnerable versions in security-critical contexts until a fix is available.