CVE-2025-11677Network attack vectorHinoki check available

Server crash via freed WebSocket upgrade pointer

Published Oct 20, 2025 · Updated Oct 20, 2025

Use-after-free in Warmcat libwebsockets 3 through 4.3.6 and 4.4.1 allows remote attackers to crash WebSocket servers. In lws_handshake_protocol, an invalid Upgrade header leads lws_http_transaction_completed to free wsi data before the up pointer is passed to user_callback_handle_rxflow and later strcasecmp calls. Reachability requires a server callback that handles LWS_CALLBACK_HTTP_CONFIRM_UPGRADE and operates on the pointer despite its zero length; the documented impact is service interruption.

CVSS severity6.3
Medium
EPSS probability0.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Use-after-free in Warmcat libwebsockets 3 through 4.3.6 and 4.4.1 allows remote attackers to crash WebSocket servers. In lws_handshake_protocol, an invalid Upgrade header leads lws_http_transaction_completed to free wsi data before the up pointer is passed to user_callback_handle_rxflow and later strcasecmp calls. Reachability requires a server callback that handles LWS_CALLBACK_HTTP_CONFIRM_UPGRADE and operates on the pointer despite its zero length; the documented impact is service interruption.

The record

CVE
CVE-2025-11677
Published
Oct 20, 2025
Updated
Oct 20, 2025
Vendor
libwebsockets
Product
libwebsockets
Classifications
CWE-416, CAPEC-100, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 20, 2025CVE publishedPublication date reported by the CVE source.
  2. Oct 20, 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=4.0 <=4.3.6
  2. Affected versionversion=4.0 <=4.4.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

libwebsockets · libwebsocketsversion=4.0 <=4.3.6; version=4.0 <=4.4.2

Published CVSS scores

6.3Nozomi NetworksCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

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-416Use After Free
CAPEC-100Overflow Buffers
T1499.004Application or System Exploitation

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

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Your stack

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