CVE-2025-1866Network attack vector

Memory corruption via pre-array pointer arithmetic

Published Mar 3, 2025 · Updated Mar 3, 2025

Memory-bounds error in Warmcat libwebsockets before 4.3.4 allows remote attackers to corrupt memory through crafted compressed streams. The bundled Win32 zlib inftrees.c subtracts 257 from base and extra array pointers, creating pointers before their allocated arrays before indexing them during inflate-table construction. Exposure is limited to Win32 builds that enable extensions or HTTP stream compression through non-default CMake settings, and the undefined behavior can crash or corrupt the hosting process.

CVSS severity10.0
Critical
EPSS probability0.43%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Memory-bounds error in Warmcat libwebsockets before 4.3.4 allows remote attackers to corrupt memory through crafted compressed streams. The bundled Win32 zlib inftrees.c subtracts 257 from base and extra array pointers, creating pointers before their allocated arrays before indexing them during inflate-table construction. Exposure is limited to Win32 builds that enable extensions or HTTP stream compression through non-default CMake settings, and the undefined behavior can crash or corrupt the hosting process.

The record

CVE
CVE-2025-1866
Published
Mar 3, 2025
Updated
Mar 3, 2025
Vendor
libwebsockets
Product
libwebsockets
Classifications
CWE-119, CAPEC-129, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 3, 2025CVE publishedPublication date reported by the CVE source.
  2. Mar 3, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=0 <<4.3.4 changes=[{"at":"patch 4.3.4","status":"unaffected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

libwebsockets · libwebsocketsversion=0 <<4.3.4 changes=[{"at":"patch 4.3.4","status":"unaffected"}]

Published CVSS scores

10.0GovTech CSGCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
CAPEC-129Pointer Manipulation
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo