CVE-2026-34073Network attack vector

Peer impersonation via omitted DNS constraint check

Published Mar 31, 2026 · Updated Mar 31, 2026

Certificate validation bypass in cryptography before 46.0.6 allows remote attackers to impersonate DNS peers excluded by CA constraints. The X.509 verifier applies DNS name constraints to certificate SANs but omits the separately supplied peer name, so a wildcard SAN can match a name that a parent certificate excludes. Exploitation requires an uncommon constrained-CA topology avoided by the Web PKI; successful validation accepts an unauthorized peer identity.

CVSS severity5.3
Medium
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Certificate validation bypass in cryptography before 46.0.6 allows remote attackers to impersonate DNS peers excluded by CA constraints. The X.509 verifier applies DNS name constraints to certificate SANs but omits the separately supplied peer name, so a wildcard SAN can match a name that a parent certificate excludes. Exploitation requires an uncommon constrained-CA topology avoided by the Web PKI; successful validation accepts an unauthorized peer identity.

The record

CVE
CVE-2026-34073
Published
Mar 31, 2026
Updated
Mar 31, 2026
Vendor
Python Cryptographic Authority
Product
cryptography
Classifications
CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 31, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 31, 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=< 46.0.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Python Cryptographic Authority · cryptographyversion=< 46.0.6

Published CVSS scores

5.3NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
1.7GitHub, Inc.CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U

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.

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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-295Improper Certificate Validation
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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