Cyber Resilience

CVE-2026-43861

Published
04 May 2026
Modified
17 June 2026
CVSS Score v3.1 3.7
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
EPSS Score 0.0016 6th percentile
Risk Priority 15 floored blend · peak EPSS

Summary

CVE-2026-43861 is a low-severity Improper Neutralization of Null Byte or NUL Character (CWE-158) vulnerability. Its CVSS base score is 3.7 (Low).

Operationally, ranked at the 6th 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-2 (Flaw Remediation) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

mutt before 2.3.2 does not check for '\0' in url_pct_decode.

CWE(s)
CWE-158

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

Insufficient information to map techniques.
Confidence: LOW · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2025-47812Shared CWE-158
CVE-2009-1537Shared CWE-158
CVE-2025-9648Shared CWE-158
CVE-2025-66263Shared CWE-158
CVE-2024-10921Shared CWE-158
CVE-2025-14388Shared CWE-158
CVE-2024-0408Shared CWE-158
CVE-2026-47778Shared CWE-158
CVE-2026-43859Shared CWE-158
CVE-2023-5719Shared CWE-158

Affected Assets

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • SI-10 Information Input Validation
  • SI-2 Flaw Remediation
Detect
Catch it (NIST detect / respond)
  • RA-5 Vulnerability Monitoring and Scanning
Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.2.10

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match
prevent

Directly requires validation of input data (including URL percent-decoding) to reject or neutralize illegal characters such as NUL, preventing the exact flaw described in url_pct_decode.

SI-2 Flaw Remediation good match
prevent

Mandates timely application of security-relevant patches, directly eliminating the mutt < 2.3.2 null-byte handling defect before exploitation.

RA-5 Vulnerability Monitoring and Scanning partial match
detect

Requires continuous vulnerability scanning that would identify the presence of the unpatched mutt version containing the CWE-158 flaw.

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 input neutralization and validation to prevent null-byte flaws.

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.8.29 Security testing in development and acceptance mostly match
detects

Security testing can detect null-byte flaws but does not itself implement the neutralization.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle mandates input validation and sanitization that directly prevents null-byte injection.

A.8.26 Application security requirements partial match
prevents

Application security requirements include explicit rules for neutralizing dangerous characters such as NUL.

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

Secure architecture principles reduce the likelihood of unsafe data flows but do not prescribe character neutralization.

A.8.28 Secure coding partial match
prevents

Secure coding standards explicitly require proper neutralization of null bytes and other metacharacters.

References