CVE-2026-74900
Received Received - Intake

OpenSSL pqc.py KEM Decapsulation Flaw Enables Key Recovery

Publication date: 2026-08-17

Last updated on: 2026-08-17

Assigner: VulnCheck

Description
openssl_encrypt versions before 1.4.0 contain a critical vulnerability in pqc.py where KEM decapsulation failures silently fall back to simulation mode, generating a deterministic shared secret from only 16 bytes of the private key and publicly available encapsulated key data. Attackers who obtain 16 bytes of the private key can compute the shared secret and decrypt all ciphertext, as the fallback triggers on any KEM failure without raising an error.

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Meta Information

Published
2026-08-17
Last Modified
2026-08-17
Generated
2026-08-17
AI Q&A
2026-08-17
EPSS Evaluated
N/A
NVD
CVE-2026-74900
EUVD
EUVD-2026-60117

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
openssl openssl_encrypt to 1.4.0 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-391 [PLANNED FOR DEPRECATION. SEE MAINTENANCE NOTES AND CONSIDER CWE-252, CWE-248, OR CWE-1069.] Ignoring exceptions and other error conditions may allow an attacker to induce unexpected behavior unnoticed.

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Executive Summary

This vulnerability affects openssl_encrypt versions before 1.4.0. When Key Encapsulation Mechanism (KEM) decapsulation fails, the system silently falls back to a simulation mode that generates a deterministic shared secret using only 16 bytes of the private key and publicly available data. Attackers who obtain these 16 bytes can compute the shared secret and decrypt all ciphertext.

Detection Guidance

To detect this vulnerability, check the version of openssl_encrypt installed on your system. Run: pip show openssl_encrypt or pip list | grep openssl_encrypt. If the version is below 1.4.0, the system is vulnerable.

Impact Analysis

If you use openssl_encrypt versions before 1.4.0, an attacker who steals just 16 bytes of your private key could decrypt all encrypted communications or data. The vulnerability lacks forward secrecy, meaning the same inputs always produce the same shared secret, enabling mass decryption of past and future traffic.

Compliance Impact

This vulnerability likely violates compliance requirements for data protection and encryption standards under GDPR and HIPAA. It enables unauthorized decryption of sensitive data, potentially leading to breaches of confidentiality and integrity, which are core compliance mandates.

Mitigation Strategies

Immediately upgrade openssl_encrypt to version 1.4.0 or later. If upgrading is not possible, disable the PQC simulation mode fallback in pqc.py and ensure all KEM operations raise errors on failure instead of silently degrading.

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