Cyber Resilience

CVE-2026-39087

CriticalRCE

Published: 23 April 2026

Published
23 April 2026
Modified
04 May 2026
KEV Added
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Patch
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CVSS Score v3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.0041 32.7th percentile
Risk Priority 70 floored blend · peak EPSS

Summary

CVE-2026-39087 is a critical-severity Code Injection (CWE-94) vulnerability in Ntfy (inferred from references). Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 32.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Deeper analysis

CVE-2026-39087, published on 2026-04-23, is a critical vulnerability (CVSS 9.8, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) affecting Ntfy, specifically the ntfy.sh server before version 2.21. The issue resides in the parseActions function, enabling a remote attacker to execute arbitrary code, classified under CWE-94 (Code Injection).

Any remote attacker can exploit this vulnerability over the network with low attack complexity, requiring no privileges or user interaction. Successful exploitation allows full arbitrary code execution on the targeted Ntfy server, resulting in high impacts to confidentiality, integrity, and availability.

Advisories recommend updating to Ntfy version 2.21 or later to mitigate the vulnerability. Additional details are available in the references: http://ntfy.com, http://ntfysh.com, and https://gist.github.com/MightyNawaf/5d41d6e8ead16e217f86b016002ecae5.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability details

ntfy before 2.22.0 allows SSRF because of an unanchored regular expression.

CWE(s)
CWE-94

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?

The vulnerability allows unauthenticated remote code execution on a public-facing Ntfy.sh server via code injection, directly mapping to exploitation of public-facing applications.

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

CVEs Like This One

CVE-2026-41229Shared CWE-94
CVE-2026-44262Shared CWE-94
CVE-2026-40563Shared CWE-94
CVE-2024-32641Shared CWE-94
CVE-2025-71243Shared CWE-94
CVE-2026-2052Shared CWE-94
CVE-2026-9170Shared CWE-94
CVE-2025-54451Shared CWE-94
CVE-2025-50692Shared CWE-94
CVE-2025-22204Shared CWE-94

Affected Assets

Ntfy
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inferred from references and description; NVD did not file a CPE for this CVE

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SI-2 Flaw Remediation good match
prevent

Requires timely remediation of known flaws like the code injection vulnerability in ntfy by applying patches to version 2.21 or later.

SI-10 Information Input Validation good match
prevent

Mandates validation of untrusted inputs to the parseActions function to block SSRF and code injection from unanchored regular expressions.

RA-5 Vulnerability Monitoring and Scanning partial match
detect

Enables vulnerability scanning to identify and prioritize patching of critical flaws such as CVE-2026-39087 in deployed ntfy servers.

References