CVE-2025-40907Public exploitNetwork attack vector

Code execution via overflowing FastCGI parameter lengths

Published May 16, 2025 · Updated Sep 5, 2025

Heap-based buffer overflow in FastCGI Developer's Kit 0.44 through 0.82 allows remote attackers to crash or execute code via crafted IPC data. ReadParams in libfcgi/fcgiapp.c adds two to attacker-controlled nameLen and valueLen values without rejecting integer overflow, then FCGX_GetStr copies input into the undersized allocation. Reachability requires a 32-bit build and access to the FastCGI socket through network exposure or an SSRF path; under those conditions the demonstrated result ranges from an application crash to code execution.

CVSS severity5.3
Medium
EPSS probability0.65%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in FastCGI Developer's Kit 0.44 through 0.82 allows remote attackers to crash or execute code via crafted IPC data. ReadParams in libfcgi/fcgiapp.c adds two to attacker-controlled nameLen and valueLen values without rejecting integer overflow, then FCGX_GetStr copies input into the undersized allocation. Reachability requires a 32-bit build and access to the FastCGI socket through network exposure or an SSRF path; under those conditions the demonstrated result ranges from an application crash to code execution.

The record

CVE
CVE-2025-40907
Published
May 16, 2025
Updated
Sep 5, 2025
Vendor
FastCGI
Product
FastCGI Developer's Kit
Classifications
CWE-190, CWE-122, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 16, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 5, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.44 <=0.82

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

FastCGI · FastCGI Developer's Kitversion=0.44 <=0.82

Published CVSS scores

5.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
CWE-122Heap-based Buffer Overflow
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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