Vulnerability in CPython (August 11, 2026)

unknownCVE-2026-18503

A vulnerability has been discovered in CPython. It allows an attacker to cause remote denial of service.

CSIRTS triage

vendor: CPython product: CPython Denial of service

What: A remote denial-of-service vulnerability has been discovered in CPython.
Who is affected: Systems running CPython that accept remote input triggering the DoS condition.
Urgency: Unknown severity without CVSS or exploitation details; DoS impact is typically lower priority than RCE.
Action: Apply CPython security updates when released and identify affected versions in your environment.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: CERT-FR Avis de sécurité (FR · national-cert · site)
Severity: unknown
Published: 2026-08-11
Exploitation: Not in CISA KEV at last sync
Language: Machine-translated to English — verify against the original

Original advisory: https://www.cert.ssi.gouv.fr/avis/CERTFR-2026-AVI-0994/

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-185030.12% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 2% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-18503	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for CPython

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

high[UPDATE] [high] CPython: Multiple vulnerabilitiescert-bund · 2026-08-25
medium[UPDATE] [medium] CPython: Multiple vulnerabilitiescert-bund · 2026-08-25
medium[UPDATE] [medium] CPython: Multiple vulnerabilitiescert-bund · 2026-08-25
high[NEW] [high] CPython: Vulnerability allows Denial of Servicecert-bund · 2026-08-25
medium[UPDATE] [medium] CPython: Multiple vulnerabilitiescert-bund · 2026-08-25
medium[UPDATE] [medium] CPython: Vulnerability allows file manipulationcert-bund · 2026-08-25