CVE-2026-115557: Distrust compromised intermediate certificates in ssl module

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog. That can change quickly after a public write-up; re-check if you are affected.
• Editorial verdict: Patch this week. eMudhra CA Key Compromise: Update Non-Browser TLS Clients — Anyone can mint certificates from these broken CA keys, but only clients that skip Certificate Transparency and still trust the emSign root are exposed, and only to an on-path attacker: update those trust bundles this week, build machines first.

What it is

Python has added a denylist for known compromised certificates to the "ssl" module to ensure user safety even without certificate revocation configured. Known compromised certificates will automatically be rejected regardless of the SSLContext policy configuration.

Weakness type: CWE-299.

Product: Python Software Foundation CPython · Assigned by: PSF · Published: 2026-10-24

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: passive

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).

Timeline

• 2026-10-20 — erroneo.us brief: eMudhra CA Key Compromise: Update Non-Browser TLS Clients
• 2026-10-24 — CVE record published by PSF
• 2026-10-25 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. github.com github.com
2. mail.python.org mail.python.org
3. github.com github.com
4. github.com github.com
5. github.com github.com
6. github.com github.com
7. github.com github.com
8. github.com github.com
9. github.com github.com
10. github.com github.com
11. github.com github.com
12. github.com github.com
13. github.com github.com
14. github.com github.com

Vulnerability records

1. CVE.org record CVE-2026-115557 cve.org
2. NVD entry CVE-2026-115557 nvd.nist.gov

Other references from the CVE record and advisory

1. openwall.com openwall.com
2. github.com github.com
3. emudhra.we-have-a-problem.com emudhra.we-have-a-problem.com
4. openwall.com openwall.com

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