# CVE-2026-75803: OpenSSL ChaCha20-Poly1305 and AES-OCB authentication tag bypass

Source: https://junglewise.ai/threats/cve-2026-75803-openssl-chacha20-poly1305-and-aes-ocb-authentication-tag-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-25. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-75803 · Severity: critical · CVSS 9.1 · Published 2026-08-25

OpenSSL's encryption library contains a flaw in how it validates authentication tags when decrypting empty messages using ChaCha20-Poly1305 and AES-OCB ciphers. Applications that rely on OpenSSL's EVP_Cipher() function to verify message authenticity may incorrectly accept forged or tampered messages, allowing attackers to bypass cryptographic integrity checks and potentially modify encrypted data without detection.

Technologies: [OpenSSL](https://junglewise.ai/threats/technologies/openssl). Vendors: [OpenSSL](https://junglewise.ai/threats/vendors/openssl).

## Quick answers

**Is CVE-2026-75803 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-75803 being exploited in the wild.

**How severe is CVE-2026-75803?** Critical severity, with a CVSS score of 9.1, published 25 August 2026.

**Which products and versions are affected?** OpenSSL 4.0, 3.6, 3.5, 3.4, 3.0 and likely earlier.

**Is there a fix for CVE-2026-75803?** A patch was published on 2026-08-19: Patches available via commits 119ab95 and 3621257 on GitHub Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-75803 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-75803?** Check whether you run OpenSSL at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in OpenSSL's EVP_Cipher() API when used with AEAD (Authenticated Encryption with Associated Data) ciphers ChaCha20-Poly1305 and AES-OCB. When an empty ciphertext is passed to EVP_Cipher() for decryption, the function incorrectly returns success without verifying the supplied authentication tag, violating the expected behavior of tag validation. This occurs in the built-in provider's AEAD implementations where the code takes an early exit on empty messages and skips tag comparison. The vulnerability requires only network reachability to an application using affected OpenSSL versions; an attacker can supply a corrupted or forged authentication tag that will be accepted as valid. The fix ensures these ciphers perform tag verification even for empty-ciphertext operations, aligning behavior with the streaming decryption path.

## Affected products

- OpenSSL OpenSSL 4.0, 3.6, 3.5, 3.4, 3.0 and likely earlier

## Timeline

- 2026-08-25: disclosed
- 2026-08-19: patched: Patches available via commits 119ab95 and 3621257 on GitHub

## References

- [https://github.com/openssl/openssl/commit/119ab9555dc62275bbd71f6f49529b1a44feba42](https://github.com/openssl/openssl/commit/119ab9555dc62275bbd71f6f49529b1a44feba42)
- [https://github.com/openssl/openssl/commit/3621257986e27e540bf96a11570929a6e5a9e05b](https://github.com/openssl/openssl/commit/3621257986e27e540bf96a11570929a6e5a9e05b)

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