Vulnerability · Published Aug 17, 2026 · Assigned by VulnCheck

CVE-2026-74901openssl_encrypt before 1.4.0 Authentication Bypass via AES-CTR Fallback

Critical 9.8

In plain English

A critical-severity security flaw in openssl_encrypt from jahlives. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.8Critical

Exploit odds (30 days)0.4%top 65.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

openssl_encrypt versions before 1.4.0 contain an authentication bypass vulnerability in pqc.py where AES-GCM decryption failures trigger fallback to unauthenticated AES-CTR mode. Attackers can modify ciphertext in transit to bypass integrity verification and perform bit-flipping attacks without detection.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	openssl-encrypt	1.4.0	PYSEC-2026-3773

Affected products (as reported)

Vendor	Product	Versions
jahlives	openssl_encrypt	0 – before 1.4.0

Weakness: CWE-347 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References

GitHub Security Advisory (GHSA-w4j7-wfgw-r52w) vendor-advisory
VulnCheck Advisory: openssl_encrypt before 1.4.0 Authentication Bypass via AES-CTR Fallback third-party-advisory