GHSA-6q48-6c7w-9gw2 PYSEC-2026-4320

certifi bundles emSign root CAs with compromised intermediate CA keys

Critical PyPI

Severity: 9.1 / 10; Critical · CVSS 4.0
Exploit chance (EPSS): —; No score published
Known exploited: No; Not in CISA's catalog
Weakness: CWE-295 Improper Certificate Validation
Fix: 2026.10.18; Upgrade certifi to this version or later

Description

Certifi versions before 2026.10.18 include the emSign ECC Root CA - G3 root certificate in their bundled CA store. Eight eMudhra intermediate CA certificates that chain to this root have compromised private keys and the CA has revoked them.

An attacker with one of the compromised keys can issue valid-looking certificates for any hostname. If the attacker is also on-path, they can intercept or modify TLS traffic from clients that trust the certifi bundle. Examples include requests, urllib3 and pip, and the Python.org macOS installer.

Certifi 2026.10.18 removed all emSign roots from the bundle. Certifi 2026.10.19 restored the emSign roots that are not affected. Upgrade to 2026.10.19 or later, and rebuild container images that vendor certifi.

Affected versions

PyPI

Package	Vulnerable	Fixed in
certifi	`>= 2019.03.09, < 2026.10.18`	`2026.10.18`
certifi	`>= 2019.03.09, < 2026.10.18`	`2026.10.18`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

certifi PyPI → `2026.10.18`

pip

pip install --upgrade "certifi>=2026.10.18"

poetry

poetry add "certifi>=2026.10.18"

uv

uv add "certifi>=2026.10.18"

Severity breakdown

CVSS 4.0 9.1

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: High
Attack requirements: Present
Privileges required: None
User interaction: None
Confidentiality (vulnerable system): High
Integrity (vulnerable system): High
Availability (vulnerable system): None
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

Weakness

CWE-295: Improper Certificate Validation

The product does not validate, or incorrectly validates, a certificate.

How to prevent it

Architecture and Design, Implementation: Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key.
Implementation: If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.

References

Advisories

Packages

Timeline

Oct 20, 2026 Published
Oct 30, 2026 Last updated by the source

Advisory	Severity	Why it's related
GHSA-248v-346w-9cwc Certifi removes GLOBALTRUST root certificate	High	Also affects certifi
GHSA-xqr8-7jwr-rhp7 Removal of e-Tugra root certificate	Critical	Also affects certifi
GHSA-43fp-rhv2-5gv8 Certifi removing TrustCor root certificate	High	Also affects certifi
GHSA-4487-j8r4-4g2f Forge: verifyCertificateChain() removes trusted CA certificates with the same subject from the CA store	Low	Same weakness, CWE-295
GHSA-5x38-2vff-x55p Forge: X.509 basicConstraints bypass in verifyCertificateChain() via deprecated extension OIDs 2.5.29.10 and 2.5.29.13	High	Same weakness, CWE-295
EEF-CVE-2026-115693 Custom cacerts or cacertfile do not restrict trust to the pinned CA in hackney	Not rated yet	Same weakness, CWE-295
GHSA-2m5v-pch6-74hx undici vulnerable to TLS certificate validation bypass via dropped tls options in Agent	Critical	Same weakness, CWE-295
GHSA-vrv5-2jg9-4mmr Microsoft Security Advisory CVE-2026-96222 - .NET Spoofing Vulnerability	High	Same weakness, CWE-295

Is this in your code?

MergeHarbor checks every repository's dependencies against this database, ranks what matters by exploitability and reachability, routes it to the owning team and opens the fix pull request.

Check your repos with MergeHarbor