CVE-2026-34182Network attack vector

Message forgery via unchecked CMS authentication parameters

Published Jun 9, 2026 · Updated Jun 9, 2026

Improper integrity validation in OpenSSL CMS AuthEnvelopedData processing allows attackers to forge encrypted messages via crafted inputs. ossl_cms_EncryptedContent_init_bio accepts non-AEAD ciphers for authenticated envelopes and permits AEAD tags as short as one byte, so CMS_decrypt() can report success without sound authentication. Exploitation requires either a captured legitimate envelope and a visible decryption result for the CEK oracle, or repeated forgery attempts; FIPS modules are unaffected.

CVSS severity9.1
Critical
EPSS probability0.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper integrity validation in OpenSSL CMS AuthEnvelopedData processing allows attackers to forge encrypted messages via crafted inputs. ossl_cms_EncryptedContent_init_bio accepts non-AEAD ciphers for authenticated envelopes and permits AEAD tags as short as one byte, so CMS_decrypt() can report success without sound authentication. Exploitation requires either a captured legitimate envelope and a visible decryption result for the CEK oracle, or repeated forgery attempts; FIPS modules are unaffected.

The record

CVE
CVE-2026-34182
Published
Jun 9, 2026
Updated
Jun 9, 2026
Vendor
OpenSSL Project
Product
OpenSSL
Classifications
CWE-354, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=3.0.0 <3.0.21
  2. Affected versionversion=3.4.0 <3.4.6
  3. Affected versionversion=3.5.0 <3.5.7
  4. Affected versionversion=3.6.0 <3.6.3
  5. Affected versionversion=4.0.0 <4.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenSSL Project · OpenSSLversion=3.0.0 <3.0.21; version=3.4.0 <3.4.6; version=3.5.0 <3.5.7; version=3.6.0 <3.6.3; version=4.0.0 <4.0.1

Published CVSS scores

9.1CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-354Improper Validation of Integrity Check Value
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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