cryptography has incomplete DNS name constraint enforcement on peer names

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

1.7 · 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 · score source

EPSS

• CVE-2026-34073: 0.23% estimated exploitation activity in the next 30 days; percentile 13.54 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary In versions of cryptography prior to 46.0.5, DNS name constraints were only validated against SANs within child certificates, and not the "peer name" presented during each validation. Consequently, cryptography would allow a peer named bar.example.com to validate against a wildcard leaf certificate for .example.com, even if the leaf's parent certificate (or upwards) contained an excluded subtree constraint for bar.example.com. This behavior resulted from a gap between RFC 5280 (which defines Name Constraint semantics) and RFC 9525 (which defines service identity semantics): put together, neither states definitively whether Name Constraints should be applied to peer names. To close this gap, cryptography now conservatively rejects any validation where the peer name would be rejected by a name constraint if it were a SAN instead. In practice, exploitation of this bypass requires an uncommon X.509 topology, one that the Web PKI avoids because it exhibits these kinds of problems.…

Published by the source

27 Mar 2026, 19:56 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:42 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m959-cc7f-wv43

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-m959-cc7f-wv43

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-34073

Advisory: cryptography has incomplete DNS name constraint enforcement on peer names
IDs: CVE-2026-34073, GHSA-m959-cc7f-wv43
Record: https://patchnext.com/advisories/cve-2026-34073 (revision 3, source checked 26 Oct 2026, 13:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 1.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: cryptography 46.0.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI cryptography: affected < 46.0.6; fixed in 46.0.6

## Suggested inspection (read-only)
- `python -m pip show cryptography`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on cryptography.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-m959-cc7f-wv43 (OSV record GHSA-m959-cc7f-wv43 lists affected ranges: PyPI cryptography >=0 <46.0.6 (fixed))
- Verified: https://github.com/advisories/GHSA-m959-cc7f-wv43 (GitHub-reviewed advisory GHSA-m959-cc7f-wv43 lists affected ranges: PyPI cryptography >=0 <46.0.6)

Commands are suggestions: review each one before running it.