High

Apache HttpComponents Core: HPackDecoder Unlimited Header List Size Before SETTINGS ACK

Disclosed: 01.07.2026
Updated: 11.10.2026 13:20

Allocation of resources without limits or throttling in the HTTP/2 HPACK decoder in Apache HttpComponents Core (5.4.2 and earlier, 5.5-beta1 and earlier) allows an remote attacker to cause a denial of service through memory exhaustion by sending oversized compressed header blocks before the HTTP/2 SETTINGS acknowledgement causes the configured header list size limit to be applied.

Affected software

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Platform	Package	Vulnerable versions	Fixed in
Java / Kotlin (Maven)	org.apache.httpcomponents.core5:httpcore5-h2	< 5.4.3, >= 5.5-alpha1, < 5.5-beta2	5.4.3, 5.5-beta2

References

CVSS score 7.5/10

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-400
Platform: Java / Kotlin (Maven)
Package: org.apache.httpcomponents.core5:httpcore5-h2
Disclosed: 01.07.2026
Updated: 11.10.2026 13:20

Sources and licenses

OSV / GitHub Advisory Database - GHSA-v3jc-474w-2wm6 - CC BY 4.0

Vulnerability history: org.apache.httpcomponents.core5:httpcore5-h2

All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.

This is the only known vulnerability of this package.

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