CVE-2025-8671 (CVSS 7.5)

Description

A mismatch caused by client-triggered server-sent stream resets between HTTP/2 specifications and the internal architectures of some HTTP/2 implementations may result in excessive server resource consumption leading to denial-of-service (DoS). By opening streams and then rapidly triggering the server to reset them—using malformed frames or flow control errors—an attacker can exploit incorrect stream accounting. Streams reset by the server are considered closed at the protocol level, even though backend processing continues. This allows a client to cause the server to handle an unbounded number of concurrent streams on a single connection. This CVE will be updated as affected product details are released.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-404 CWE-404

References

Other References

https://galbarnahum.com/made-you-reset https://github.com/h2o/h2o/commit/4729b661e3c6654198d2cc62997e1af58bef4b80 https://github.com/h2o/h2o/security/advisories/GHSA-mrjm-qq9m-9mjq https://gitlab.isc.org/isc-projects/bind9/-/issues/5325 https://kb.cert.org/vuls/id/767506 https://support2.windriver.com/index.php?page=security-notices https://varnish-cache.org/security/VSV00017.html https://www.fastlystatus.com/incident/377810 https://www.suse.com/support/kb/doc/?id=000021980 http://www.openwall.com/lists/oss-security/2025/08/13/6

Frequently Asked Questions

What is CVE-2025-8671? +

A mismatch caused by client-triggered server-sent stream resets between HTTP/2 specifications and the internal architectures of some HTTP/2 implementations may result in excessive server resource consumption leading to denial-of-service (DoS). By opening streams and then rapidly triggering the server to reset them—using malformed frames or flow control errors—an attacker can exploit incorrect stream accounting. Streams reset by the server are considered closed at the protocol level, even though backend processing continues. This allows a client to cause the server to handle an unbounded number of concurrent streams on a single connection. This CVE will be updated as affected product details are released. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2025-8671? +

CVE-2025-8671 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

How do I check if I'm vulnerable to CVE-2025-8671? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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