CVE-2026-59837: Stack-Based Buffer Overflow in FortiOS Log Report Generation

HERMES

HERMES THREAT SCORE & STACK OVERFLOW RISKS

Target: Fortinet FortiOS / FortiPAM / FortiProxy Report Engine Daemon

Confidence: 96%

78 / 100

HIGH

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 15 / 20

Threat Activity 13 / 20

Weaponization 16 / 20

Exposure 15 / 20

Prevalence 19 / 20

Impact 19 / 20

Exploit Maturity 14 / 20

Attack Chain Potential 18 / 20

⚖️ Divergence & Operational Rationale

Hermes assesses CVE-2026-59837 at HTS 78 (High). Although triggering the buffer overflow requires an authenticated administrative profile, exploiting it can bypass daemon privileges to achieve arbitrary machine instructions execution on the firewall management plane if memory hardening mitigations are bypassed.

🕸️ Connected Knowledge Graph & Provenance

CVE-2026-59837: Stack-Based Buffer Overflow in FortiOS Log Report GenerationVULNERABILITY

Connected Nodes: 1

Active Relationships (Outgoing)

→ affectsPRODUCTFortinet FortiOS Gateway

98% VERY_HIGH

Software platform affected by security vulnerabilities and agentic attack patterns.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in Fortinet FortiOS Gateway documented in Hermes dossier.”

Supporting Verified Evidence:

• [vulnerability_report]
• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

Stack-based Buffer Overflow in Log Reporting

CVSS v3.1: 6.6 Medium / 7.2 Adjusted (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H) / CWE-121: Stack-based Buffer Overflow.
Disclosed in Fortinet security bulletins. A stack-based buffer overflow in the log report generation service allows an authenticated administrative attacker to trigger memory corruption and execute arbitrary code or shell commands via crafted HTTP/HTTPS management requests. Addressed in FortiOS 7.4.2 and 7.2.7.

Executive Summary

Fortinet patched CVE-2026-59837, a memory corruption vulnerability impacting the administrative report generation component across FortiOS, FortiPAM, and FortiProxy.

When compiling statistical log summaries or generating formatted reporting documents, the target binary allocates a fixed-size stack frame buffer for report metadata headers. Passing oversized or maliciously formatted parameters causes stack frame corruption, overwriting return pointers and leading to denial of service or potential arbitrary code execution.

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1. Metadata & Attack Surface

Metric	Technical Specification	Operational Impact
CVE Identifier	CVE-2026-59837	Standardized vulnerability identifier
Vendor / Software	Fortinet / FortiOS, FortiPAM, FortiProxy	Enterprise network security platforms
Affected Releases	FortiOS 7.4.0–7.4.1, 7.2 (all versions prior to 7.2.7)	Management report engine
Fixed Releases	FortiOS 7.4.2, 7.2.7, FortiPAM 1.8.3, FortiProxy 7.4.14	Vendor firmware upgrades
Associated CWE	CWE-121: Stack-based Buffer Overflow	Memory safety violation
Prerequisites	Authenticated administrator on web management plane	Web UI / HTTPS port 443

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2. Technical Root Cause Analysis

The flaw exists within reportd / report compilation subroutines where formatting parameters are copied using unsafe string formatting functions (sprintf() / strcpy()) without bounds enforcement.

Stack Buffer Overflow Layout:

  Stack Frame: generate_log_report()
  ┌────────────────────────────────────────────────────────┐
  │ Local Stack Buffer [Size: 1024 bytes]                  │
  ├────────────────────────────────────────────────────────┤
  │ Stack Canary (Guard Value)                             │  ◄── Overwritten by attacker payload
  ├────────────────────────────────────────────────────────┤
  │ Saved Frame Pointer (EBP / RBP)                        │  ◄── Corrupted
  ├────────────────────────────────────────────────────────┤
  │ Saved Return Address (EIP / RIP)                       │  ◄── Hijacked execution control
  └────────────────────────────────────────────────────────┘

An authenticated user with report configuration privileges can supply an excessively long title, filter expression, or column description string. When processed, the buffer overflows the allocated frame, crashing the daemon or redirecting control flow.

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3. Mitigation & Remediation Playbook

1. Apply Firmware Patch:
   Upgrade FortiOS to 7.4.2 or 7.2.7+. For FortiProxy, upgrade to 7.4.14+.
2. Restrict Report Generation Privileges:
   Review administrator access profiles under System > Admin Profiles and remove report generation permissions from delegated operators.
3. Isolate Management Access:
   Never permit untrusted network zones or WAN interfaces to access the administrative web interface.