CVE-2026-4258

High

Published: 17 March 2026

Published

17 March 2026

Modified

17 March 2026

KEV Added

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Patch

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CVSS Score 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Score 0.0002 4.8th percentile

Risk Priority 15 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-4258 is a high-severity Improper Verification of Cryptographic Signature (CWE-347) vulnerability. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Credential Access (T1212); ranked at the 4.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SC-12 (Cryptographic Key Establishment and Management) and SI-10 (Information Input Validation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploitation for Credential Access (T1212) and 1 other technique. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

preventrecover

Directly requires timely identification, reporting, and correction of the specific flaw in sjcl's ECDH point-on-curve validation via available patch to prevent private key recovery.

SI-10 Information Input Validation good match

prevent

Mandates validation of information inputs such as ECDH public keys to detect and reject crafted off-curve points, addressing the core vulnerability.

SC-12 Cryptographic Key Establishment and Management good match

prevent

Requires approved cryptographic key establishment techniques per NIST SP 800-56A that include elliptic curve point validation, preventing exploitation through invalid public keys in ECDH.

MITRE ATT&CK Enterprise TechniquesAI

T1212 Exploitation for Credential Access Credential Access

Adversaries may exploit software vulnerabilities in an attempt to collect credentials.

attack.mitre.org →

T1552.004 Private Keys Credential Access

Adversaries may search for private key certificate files on compromised systems for insecurely stored credentials.

attack.mitre.org →

Why these techniques?

Vulnerability enables remote recovery of ECDH private keys via crafted inputs and missing curve validation (direct credential theft); maps to exploitation for credential access and private key compromise.

Confidence: MEDIUM · MITRE ATT&CK Enterprise v18.1

NVD Description

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.

Deeper analysisAI

CVE-2026-4258 is an Improper Verification of Cryptographic Signature vulnerability (CWE-347, CWE-325) affecting all versions of the sjcl JavaScript cryptographic library. It arises from missing point-on-curve validation in the sjcl.ecc.basicKey.publicKey() function, enabling attackers to recover a victim's ECDH private key. The issue has a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N) and was published on 2026-03-17.

A network-based attacker requires no privileges or user interaction to exploit this vulnerability. By sending crafted off-curve public keys to a victim and observing the resulting ECDH outputs, the attacker can recover the private key. The dhJavaEc() function exacerbates the issue by directly returning the raw x-coordinate of the scalar multiplication result without hashing, providing a plaintext oracle that does not rely on decryption feedback.

Mitigation is available via a patch in the sjcl repository at commit ee307459972442a17beebc29dc331fffd8aff796, which addresses the point validation flaw. Further details, including a proof-of-concept, are provided in the GitHub gist at https://gist.github.com/Kr0emer/2560f98edb10b0b34f2438cd63913c47 and the Snyk advisory at https://security.snyk.io/vuln/SNYK-JS-SJCL-15369617. Practitioners using sjcl should update to the patched version and audit ECDH implementations for similar validation gaps.