CVE-2025-5399: WebSocket endless loop

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2025-06-07 · updated 2026-06-17
Weakness: CWE-835

Description

Due to a mistake in libcurl's WebSocket code, a malicious server can send a particularly crafted packet which makes libcurl get trapped in an endless busy-loop. There is no other way for the application to escape or exit this loop other than killing the thread/process. This might be used to DoS libcurl-using application.

Affected products

curl: from 8.13.0 before 8.14.1 — fixed in 8.14.1

How to fix

Upgrade to a fixed version: curl 8.14.1. Check the vendor advisory for mitigations.

References

https://curl.se/docs/CVE-2025-5399.html
https://curl.se/docs/CVE-2025-5399.json
https://hackerone.com/reports/3168039
http://www.openwall.com/lists/oss-security/2025/06/04/2

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