CVE-2026-34182 CMS AuthEnvelopedData Processing May Accept Forged Messages
Attackers can bypass integrity checks or recover keys in OpenSSL CMS AuthEnvelopedData processing by manipulating cipher and tag length fields.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-34182?
CVE-2026-34182 is a critical vulnerability in Openssl Openssl, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Issue Summary: Cryptographic Message Services (CMS) processing fails to perform sufficient input validation on the cipher and tag length fields of AuthEnvelopedData containers, leading to various potential compromises.
Impact Summary: Attackers making use of these vulnerabilities may achieve key-equivalent functionality for a given CMS recipient and/or bypass integrity validation for a given message.
In one use case, an attacker may send a CMS message containing AuthEnvelopedData with the cipher specified as a non-AEAD cipher. OpenSSL erroneously allows this selection, and attempts to decrypt and validate the message.
An on-path attacker who captures one legitimate AES-GCM AuthEnvelopedData addressed to the victim can re-emit it with the recipientInfos set left byte-for-byte intact, so the victim's private key still unwraps the genuine CEK (the content-encryption key), but with the inner OID rewritten to AES-256-OFB (Output Feedback Mode, an unauthenticated keystream mode) and with an attacker-chosen IV and ciphertext. The victim initializes AES-256-OFB under the real CEK, never consults the MAC field, and CMS_decrypt() returns success.
If the application under attack responds to the attacker with any indicator showing success or failure of the decryption effort, it is possible for the attacker to use this as an oracle to obtain key equivalent functionality for the CEK used for the chosen recipient of the message.
In another use case, an attacker can reduce the tag length of the chosen AEAD cipher for a given AuthEnvelopedData container to be a single byte long, allowing an attacker to brute force CMS decryption, producing an integrity bypass for applications that trust CMS_decrypt() to reject modified content.
The FIPS modules are not affected by this issue.
Weakness: CWE-354
Which versions are affected by CVE-2026-34182?
It affects 1 product.
Products include Openssl Openssl.
How do I fix CVE-2026-34182?
Apply the vendor's patch.
Is CVE-2026-34182 being exploited?
There is no known exploitation of CVE-2026-34182 in the wild and no public exploit code.
Other vulnerabilities in Openssl Openssl
Sources
Also known as ALPINE-CVE-2026-34182, AZL-89802, AZL-89861, AZL-89931, BELL-CVE-2026-34182, DEBIAN-CVE-2026-34182 and 6 more.