CVE-2025-5399Public exploitNetwork attack vector

Application hang via stalled WebSocket auto-pong

Published Jun 7, 2025 · Updated Jun 9, 2025

Denial of service in libcurl 8.13.0 through 8.14.0 allows remote attackers controlling a WebSocket server to hang applications. In lib/ws.c, curl_ws_send retries a blocked auto-pong send without advancing sendbuf_payload, so the callback loop never yields. The application must use libcurl WebSockets with auto-pong enabled and connect to the malicious server; the curl command-line tool is unaffected.

CVSS severity7.5
High
EPSS probability1.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in libcurl 8.13.0 through 8.14.0 allows remote attackers controlling a WebSocket server to hang applications. In lib/ws.c, curl_ws_send retries a blocked auto-pong send without advancing sendbuf_payload, so the callback loop never yields. The application must use libcurl WebSockets with auto-pong enabled and connect to the malicious server; the curl command-line tool is unaffected.

The record

CVE
CVE-2025-5399
Published
Jun 7, 2025
Updated
Jun 9, 2025
Vendor
curl
Product
curl
Classifications
CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 7, 2025CVE publishedPublication date reported by the CVE source.
  2. Jun 9, 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=8.13.0 <=8.13.0
  2. Affected versionversion=8.14.0 <=8.14.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=8.13.0 <=8.13.0; version=8.14.0 <=8.14.0

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A: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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Endpoint Denial of Service: Application or System Exploitation DoS

Public exploit references

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Technologies

Your stack

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Your stack

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