Critical severity · published Jun 9, 2026
CVE-2026-34182
CMS AuthEnvelopedData Processing May Accept Forged Messages
9.1
CVSS
1.1%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.1% · higher than 64% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
OP
OpenSSL · OpenSSL
4.0.0 before 4.0.1; 3.6.0 before 3.6.3; 3.5.0 before 3.5.7; 3.4.0 before 3.4.6; 3.0.0 before 3.0.21 · source: vendor, NVD
In the news
VulnerabilityLow
ZDI-26-790: OpenSSL CMS AuthEnvelopedData Improper Validation of Integrity Check Value Vulnerability
This vulnerability allows network-adjacent attackers to tamper with CMS AuthEnvelopedData messages on affected installations of OpenSSL. An attacker must first obtain the ability to modify CMS AuthEnvelopedData messages in order to exploit this vulnerability. The ZDI has assigned a CVSS rating of 3.1. The following CVEs are assigned: CVE-2026-34182.
Oct 22, 2026·Zero Day Initiative
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34182
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-34182
Patch
https://github.com/openssl/openssl/commit/03c1f4d45fb963aee7d5833390c507cd290182bc
Patch
https://github.com/openssl/openssl/commit/439ed7d2c0962ce964482727264668bf277c333f
Patch
https://github.com/openssl/openssl/commit/7947e6a81eb8776802f159fb6762cb7fcf7e34c7
Patch
https://github.com/openssl/openssl/commit/9fd97f8cfdc2c0be214998de3b2b55c8edf6c7ac
Patch
https://github.com/openssl/openssl/commit/d2ca86bcd43e4f17d899f347101766b6107676e0
Vendor Advisory
https://openssl-library.org/news/secadv/20260609.txt
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