certifi bundles emSign root CAs with compromised intermediate CA keys
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Fix
- Fixed in 2026.10.18
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
The certifi Python package, which supplies the trusted certificate list used by tools like requests, urllib3, pip, and the Python.org macOS installer, includes a root certificate whose subordinate keys were compromised. An attacker holding one of these keys could create convincing fake certificates for any website and, if positioned between a user and a server, read or alter encrypted traffic.
Summarized by anthropic/claude-haiku-5.5. Verify details against the original sources.
Read the original 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.
Timeline
- Advisory published10 days
- Record last updated
Affected versions
- certifiPyPI
From 2019.03.09 · fixed in 2026.10.18