Cookie Attribute Injection via Unescaped Semicolons in http.cookies.Morsel

published 2026-11-12 2d ago modified 2026-11-12 2d ago also EUVD-2026-124537

cvss: 2.3; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 23%
public exploits: 0; none known

The http.cookies.Morsel class allows separator semicolons in attribute values and includes them verbatim in all output formats. An attacker who can control these values could use this to relax the cookie's Domain or SameSite restrictions.

Patch / fix

fixed in 1 links 1

Python Software Foundation CPython 3.16.0

github.com/python/cpython#161711 pull request

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Exploit prediction

0.31% chance of exploitation in the next 30 days, higher than 23% of all scored CVEs (FIRST EPSS, 2026-11-14).

CVSS scores

assigned by	version	score	vector
CNA	4.0	2.3	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
CNA	4.0	2.3	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

Python Software Foundation CPython

Classification

Weakness

CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component

References

Sources

CVE List CVE-2026-16052
NVD CVE-2026-16052

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