CVE-2026-85393 in node-forge
Summary
by MITRE • 09/03/2026
node-forge through 1.4.0 fails to validate element count in nested DigestAlgorithm sequences during RSA PKCS#1 v1.5 signature verification. Attackers can embed garbage bytes inside the DigestAlgorithm sequence to forge valid signatures for arbitrary messages using low-exponent RSA keys. This is an incomplete fix for CVE-2026-33894.
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Analysis
by VulDB Data Team • 09/03/2026
The vulnerability identified in node-forge versions through 1.4.0 represents a critical failure in the cryptographic validation logic during RSA PKCS#1 v1.5 signature verification processes. Specifically, the library fails to properly validate the element count within nested DigestAlgorithm sequences embedded in the ASN.1 structure of the signature data. This flaw allows an attacker to manipulate the internal structure of the signed message by injecting garbage bytes or malformed elements into the DigestAlgorithm sequence without triggering a validation error. The root cause lies in insufficient parsing rigor, where the implementation does not strictly enforce the expected length and composition rules for these nested sequences as defined by cryptographic standards.
This technical flaw has severe operational implications, particularly when low-exponent RSA keys are utilized. In such scenarios, an attacker can exploit this incomplete validation to forge valid signatures for arbitrary messages that were never intended to be signed. By carefully crafting a malicious payload that exploits the lack of element count verification, the adversary can bypass integrity checks and authentication mechanisms relying on these digital signatures. This capability effectively undermines the non-repudiation and authenticity guarantees provided by RSA PKCS#1 v1.5 signing operations, potentially leading to unauthorized access, data tampering, or privilege escalation in systems dependent on this library for secure communications.
The issue is classified as an incomplete fix for CVE-2026-33894, indicating that previous remediation efforts did not fully address the underlying parsing weaknesses within the ASN.1 decoder. This suggests a broader pattern of insufficient input validation in cryptographic libraries where edge cases in complex nested structures are overlooked. The vulnerability aligns with CWE-20 Improper Input Validation and specifically relates to issues involving ambiguous or malformed data handling during protocol implementation. From an offensive security perspective, this technique maps to ATT&CK techniques related to signature forgery and exploitation of asymmetric cryptography implementations, highlighting the risk posed by weak validation in cryptographic primitives.
To mitigate this vulnerability, immediate updates to node-forge are required if a patched version is available that addresses the specific parsing logic for DigestAlgorithm sequences. Organizations relying on this library should assess their exposure by identifying all components using RSA PKCS#1 v1.5 signatures and verifying whether low-exponent keys are in use, as these present the highest risk profile. In the interim, implementing strict input validation at the application layer or switching to more robust cryptographic libraries that adhere strictly to RFC 8017 standards for ASN.1 parsing can reduce exposure. Long-term remediation should involve migrating away from PKCS#1 v1.5 signatures in favor of PSS padding schemes, which offer stronger security guarantees against such structural manipulation attacks and are less susceptible to encoding-based exploits.