Cyber Resilience

CVE-2026-9354

Published
24 May 2026
Modified
23 July 2026
CVSS Score v4 5.5
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:P/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 0.0034 26th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2026-9354 is a medium-severity Injection (CWE-74) vulnerability. Its CVSS base score is 5.5 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 26th 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

A vulnerability was detected in NousResearch hermes-agent up to 2026.4.16. The affected element is an unknown function of the component Slack Agent/Mattermost Agent. The manipulation of the argument format_message results in escaping of output. The attack can be executed remotely.…

more

The exploit is now public and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

CWE(s)
CWE-74CWE-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?

Remote injection flaw (CWE-74/116) via format_message in exposed Slack/Mattermost agent directly enables exploitation of a public-facing application.

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

Likely ATT&CK TechniquesAI

Techniques this vulnerability likely enables, inferred from its description, weakness type, and attributed-actor tradecraft. Confidence is per-technique.

T1059 Command and Scripting Interpreter Executionconfidence: MEDIUM
Improper output escaping in message formatting could allow crafted input to be interpreted as commands or scripts by the Slack/Mattermost agent.
attack.mitre.org →
inferred from description + CWE · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2025-56266Shared CWE-116, CWE-74
CVE-2026-29777Shared CWE-74
CVE-2026-45344Shared CWE-74
CVE-2026-44455Shared CWE-74
CVE-2026-1089Shared CWE-74
CVE-2026-29085Shared CWE-74
CVE-2026-26002Shared CWE-74
CVE-2026-41234Shared CWE-74
CVE-2026-5797Shared CWE-74
CVE-2025-8154Shared CWE-74

Affected Assets

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • SI-10 Information Input Validation
  • SI-15 Information Output Filtering
  • AC-4 Information Flow Enforcement
Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.1.2
  • V1.2.1
  • V1.2.3
  • V1.2.5

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match
prevent

Directly requires validation and sanitization of inputs to the format_message argument, preventing the improper neutralization defined by CWE-74.

SI-15 Information Output Filtering good match
prevent

Requires filtering/sanitization of output (escaping) before it is sent to Slack/Mattermost, directly addressing the CWE-116 weakness in the agent.

AC-4 Information Flow Enforcement partial match
prevent

Enforces information flow rules that can mandate encoding or sanitization when data crosses the boundary to external messaging agents.

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 validation and output encoding that prevent injection 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.8.28 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

Security testing in development catches injection vulnerabilities before release.

A.8.15 Logging partial match
detects

Logging supports detection of injection attempts but does not prevent the weakness.

A.8.16 Monitoring activities partial match
detects

Monitoring activities can identify active injection attacks after they occur.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle mandates input validation and output encoding that directly prevent injection flaws.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly call for controls against injection attacks in software design.

References