Cyber Resilience

CVE-2026-59838

XSS in Fortinet Fortisiem 6.4.0 – 7.2.7

XSS
Published
15 July 2026
Modified
15 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 5.9
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L
EPSS Score 0.0014 4th percentile
Risk Priority 38 floored blend · peak EPSS

Summary

CVE-2026-59838 is a medium-severity Basic XSS (CWE-80) vulnerability in Fortinet Fortisiem. Its CVSS base score is 5.9 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Content Injection (T1659); ranked at the 4th 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 SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — 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 improper neutralization of script-related html tags in a web page (basic xss) vulnerability in Fortinet FortiSIEM 7.4.0, FortiSIEM 7.3.0 through 7.3.4, FortiSIEM 7.2.0 through 7.2.6, FortiSIEM 7.1 all versions, FortiSIEM 7.0 all versions, FortiSIEM 6.7 all versions, FortiSIEM 6.6…

more

all versions, FortiSIEM 6.5 all versions, FortiSIEM 6.4 all versions may allow attacker to execute unauthorized code or commands via <insert attack vector here>

CWE(s)
CWE-80

Related Threats

MITRE ATT&CK Enterprise Techniques

T1659 Content Injection Initial Access
Adversaries may gain access and continuously communicate with victims by injecting malicious content into systems through online network traffic.
attack.mitre.org →
T1539 Steal Web Session Cookie Credential Access
An adversary may steal web application or service session cookies and use them to gain access to web applications or Internet services as an authenticated user without needing credentials.
attack.mitre.org →
T1189 Drive-by Compromise Initial Access
Adversaries may gain access to a system through a user visiting a website over the normal course of browsing.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-27780Same product: Fortinet Fortisiem
CVE-2026-25972Same product: Fortinet Fortisiem
CVE-2025-58324Same product: Fortinet Fortisiem
CVE-2023-40723Same product: Fortinet Fortisiem
CVE-2023-36551Same product: Fortinet Fortisiem
CVE-2023-41676Same product: Fortinet Fortisiem
CVE-2023-45585Same product: Fortinet Fortisiem
CVE-2024-52969Same product: Fortinet Fortisiem
CVE-2024-23109Same product: Fortinet Fortisiem
CVE-2024-23108Same product: Fortinet Fortisiem

Affected Assets

fortinet
fortisiem
7.4.0 · 6.4.0 — 7.2.7 · 7.3.0 — 7.3.5

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.2.1
  • V1.3.1
  • V1.3.3
  • V1.3.4

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can discover missing or incorrect neutralization of script tags through targeted XSS test cases.

SI-10 Information Input Validation good match

Input validation explicitly requires checking and neutralizing untrusted web inputs containing script-related characters before they reach a downstream renderer.

SA-8 Security and Privacy Engineering Principles partial match

Secure engineering principles include mandatory output encoding and neutralization of HTML metacharacters to stop injection at the source.

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 output encoding and input validation that prevent basic XSS.

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
finds

Security testing in development catches unneutralized script tags before release.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates input validation and output encoding that directly prevent basic XSS.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly call for neutralization of script-related HTML tags.

A.8.28 Secure coding partial match
prevents

Secure coding standards require proper escaping of <, >, & to block XSS.

A.8.23 Web filtering none match
none

Web filtering can block some reflected XSS payloads at the network edge.

References