## OpenSSL CVE-2026-28386: AES-CFB128 Out-of-Bounds Read Vulnerability in AVX-512/VAES Systems
A memory-safety vulnerability has been identified in OpenSSL's AES-CFB128 implementation, cataloged as CVE-2026-28386 by the National Vulnerability Database. The flaw enables an out-of-bounds read of up to 15 bytes during encryption or decryption operations on systems equipped with AVX-512 and VAES hardware support. Under specific conditions, this can trigger a process crash, creating a potential Denial-of-Service vector. Crucially, the over-read bytes are not written to output, and no information disclosure occurs as a result of the vulnerability.

The vulnerability's reach is constrained by multiple technical prerequisites. The flawed code path activates only when processing partial cipher blocks—specifically when a prior operation left an incomplete block and the subsequent call provides fewer bytes than required to complete it. Additionally, the input buffer must be positioned at a memory page boundary with the following page unmapped. CFB mode itself sees limited deployment in production environments, and notably, it is absent from TLS and DTLS protocols, which rely on CBC, GCM, CCM, or ChaCha20-Poly1305 instead. OpenSSL's security team has assessed the severity as Low given these compounding limitations.

Organizations running OpenSSL on AVX-512/VAES-enabled systems should monitor official OpenSSL security advisories for patch releases addressing this issue. While exploitation requires an unlikely confluence of hardware configuration and input conditions, any out-of-bounds memory access in cryptographic code carries reputational and operational risk. Security teams are advised to inventory affected deployments and evaluate patching timelines against broader vulnerability management priorities.
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- **Source**: GitHub Issues
- **Sector**: The Lab
- **Tags**: CVE-2026-28386, OpenSSL, AES-CFB128, out-of-bounds read, AVX-512
- **Credibility**: unverified
- **Published**: 2026-04-23 23:54:16
- **ID**: 76564
- **URL**: https://whisperx.ai/en/intel/76564