CVE-2026-4258 in sjcl
Summary
by MITRE • 03/17/2026
All versions of the package sjcl are vulnerable to Improper Verification of Cryptographic Signature due to missing point-on-curve validation in sjcl.ecc.basicKey.publicKey(). An attacker can recover a victim's ECDH private key by sending crafted off-curve public keys and observing ECDH outputs. The dhJavaEc() function directly returns the raw x-coordinate of the scalar multiplication result (no hashing), providing a plaintext oracle without requiring any decryption feedback.
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Analysis
by VulDB Data Team • 03/22/2026
The vulnerability identified as CVE-2026-4258 affects the sjcl cryptographic library, specifically targeting the elliptic curve cryptography implementation within the sjcl.ecc.basicKey.publicKey() function. This flaw represents a critical weakness in the cryptographic verification process, where the library fails to properly validate whether public keys exist on the intended elliptic curve. The absence of point-on-curve validation creates a dangerous attack surface that directly violates fundamental cryptographic security principles. According to CWE-331, this vulnerability falls under improper verification of cryptographic signatures, where the system does not adequately verify the mathematical properties of cryptographic keys before using them in operations. The flaw stems from the library's design decision to omit curve validation checks, which is a well-documented security anti-pattern that has been repeatedly highlighted in cryptographic best practices.
The technical exploitation of this vulnerability occurs through a sophisticated attack vector involving crafted off-curve public keys that are deliberately constructed to bypass normal validation mechanisms. When an attacker sends such malicious keys to a victim's system, the sjcl library processes these inputs without proper curve validation, allowing the attacker to observe the resulting ECDH outputs. The dhJavaEc() function serves as the primary attack surface because it directly returns the raw x-coordinate of scalar multiplication results without any hashing or additional processing. This exposes a plaintext oracle vulnerability where the attacker can directly observe the mathematical outputs of the elliptic curve operations, effectively eliminating the cryptographic security provided by the encryption. The attack leverages the mathematical properties of elliptic curve cryptography to recover private key information through the observation of these plaintext outputs.
The operational impact of this vulnerability is severe and far-reaching, affecting any system that relies on the sjcl library for ECDH key exchange operations. The vulnerability allows for complete private key recovery without requiring any decryption feedback or access to additional system components, making it particularly dangerous for applications that use ECDH for secure communications, digital signatures, or key derivation. This weakness creates a pathway for attackers to impersonate legitimate users, decrypt sensitive communications, and compromise the confidentiality and integrity of protected data. The vulnerability affects all versions of the sjcl package, indicating a fundamental design flaw that has persisted across the library's development lifecycle. Organizations using this library in production environments face significant risk of credential compromise, data breaches, and potential system-wide security failures.
Mitigation strategies for CVE-2026-4258 require immediate action to address the root cause of the vulnerability. The primary recommendation involves implementing proper point-on-curve validation in all cryptographic operations involving elliptic curve keys, specifically ensuring that sjcl.ecc.basicKey.publicKey() function performs comprehensive curve validation before processing any public keys. Organizations should upgrade to patched versions of the sjcl library or implement custom validation routines that verify points exist on the correct elliptic curve before accepting them for cryptographic operations. Additionally, system administrators should consider implementing monitoring for unusual ECDH behavior and establish incident response procedures to detect potential exploitation attempts. The fix should also include proper hashing of ECDH outputs to prevent plaintext oracles, as recommended in the NIST SP 800-56A standard for key agreement schemes. Organizations should conduct comprehensive security assessments to identify all systems using the vulnerable library and ensure proper key rotation procedures are implemented to maintain security post-remediation.