Cyber Resilience

CVE-2026-3644

Python ≤ 3.13.13

Published
16 March 2026
Modified
30 June 2026
Patch / advisory
View advisory
CVSS Score v4 6.0
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:H/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
EPSS Score 0.0042 34th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2026-3644 is a medium-severity Improper Input Validation (CWE-20) vulnerability in Python Python. Its CVSS base score is 6.0 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 34th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) and SI-15 (Information Output Filtering) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability Data

The fix for CVE-2026-0672, which rejected control characters in http.cookies.Morsel, was incomplete. The Morsel.update(), |= operator, and unpickling paths were not patched, allowing control characters to bypass input validation. Additionally, BaseCookie.js_output() lacked the output validation applied to BaseCookie.output().

CWE(s)
CWE-20CWE-116

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Why these techniques?

Incomplete input validation bypass for control characters in http.cookies enables exploitation of public-facing Python web apps via malicious cookie values (CWE-20/116).

Confidence: MEDIUM · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-6019Same product: Python Python
CVE-2026-4519Same product: Python Python
CVE-2025-13462Same product: Python Python
CVE-2023-33595Same product: Python Python
CVE-2026-4224Same product: Python Python
CVE-2025-6075Same product: Python Python
CVE-2025-13837Same product: Python Python
CVE-2026-4360Same product: Python Python
CVE-2026-7210Same product: Python Python
CVE-2025-12084Same product: Python Python

Affected Assets

python
python
3.15.0 · ≤ 3.13.13 · 3.14.0 — 3.14.4

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • SI-10 Information Input Validation
  • SI-15 Information Output Filtering
Detect
Catch it (NIST detect / respond)
  • SI-7 Software, Firmware, and Information Integrity
Harden
Shrink the surface (DISA STIG)
  • 6 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V1.1.2
  • V1.2.1
  • V1.2.3

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match
prevent

Directly enforces validation of all input to Morsel (including update(), |=, and unpickling paths) to reject control characters as required by the incomplete fix for CVE-2026-0672.

SI-15 Information Output Filtering good match
prevent

Requires output filtering on BaseCookie.js_output() equivalent to that already present on BaseCookie.output(), blocking control-character injection in generated JavaScript.

SI-7 Software, Firmware, and Information Integrity partial match
detect

Enables integrity verification of the http.cookies module and its cookie objects to detect tampering or bypasses that allow unvalidated control characters to persist.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require and enforce input validation during development.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.28 Secure coding mostly match
prevents

Secure coding standards explicitly require correct output encoding and escaping to preserve message structure.

A.8.29 Security testing in development and acceptance mostly match
detects

Testing against a defined set of requirements and using code review plus vulnerability scanning forces validation of inputs and handling of unanticipated conditions, reducing the chance that malformed data will be accepted.

A.8.25 Secure development life cycle partial match
prevents

Secure-coding guidelines and mandatory security testing (including code scans) compel developers to validate and sanitize inputs at design and implementation time, lowering the incidence of malformed or malicious data reaching downstream components.

A.8.26 Application security requirements partial match
prevents

Mandating input controls that include integrity checks and input validation ensures that untrusted data is examined before use, blocking the root cause of many injection and malformed-data weaknesses.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Security-by-design principles explicitly call for data validation and sanitization at every layer, reducing the chance that malformed or malicious input will be processed without scrutiny.

A.8.7 Protection against malware none match
none

Regular automated validation of system software and data content, combined with scanning of all inbound files, enforces input validation at the boundary before untrusted content is processed.

References