CVE-2026-40898 quic-go: HTTP/3 QPACK Trailer Expansion Memory Exhaustion

Medium 5.3 Published 4 Jun 2026 Updated 4 Jun 2026

Attackers can cause memory exhaustion and denial of service in quic-go HTTP/3 implementations by sending malicious QPACK-encoded trailer frames.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-40898?

CVE-2026-40898 is a medium-severity denial of service vulnerability in quic-go, published on 4 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

quic-go is an implementation of the QUIC protocol in Go. Prior to version 0.59.1, an attacker can cause excessive memory allocation in quic-go's HTTP/3 client and server implementations by sending a QPACK-encoded HEADERS frame that decodes into a large trailer field section with many unique field names and/or large values. The implementation builds an `http.Header` for the corresponding `http.Request` or `http.Response`, while only enforcing limits on the size of the QPACK-compressed HEADERS frame, not on the decoded field section. This can lead to memory exhaustion. This is very similar to CVE-2025-64702. The difference is that this issue uses HTTP trailers, rather than HTTP headers, as the attack vector. A misbehaving or malicious peer can cause a denial-of-service (DoS) attack against quic-go's HTTP/3 servers or clients by triggering excessive memory allocation, potentially leading to crashes or resource exhaustion. This affects both servers and clients due to symmetric header construction. Version 0.59.1 enforces RFC 9114 decoded field section size limits for trailers as well. It incrementally decodes QPACK entries and checks the field section size after each entry, aborting the stream if an entry causes the limit to be exceeded.

Weakness: CWE-770

Which versions are affected by CVE-2026-40898?

3 open source packages ship an affected version, including github.com/quic-go/quic-go. It affects 1 product.

Package	Affected	Fixed in
`github.com/quic-go/quic-go` Go	All versions	`0.59.1`
`github.com/quic-go/quic-go` Go	All versions	`0.59.1`
`github.com/quic-go/quic-go` Go	All versions	`0.59.1`

Linux distribution packages (4)

`receptor` Red Hat:ansible_automation_platform:2.7::el10	All versions	`0:1.6.7-1.el10ap`
`receptor` Red Hat:ansible_automation_platform:2.7::el9	All versions	`0:1.6.7-1.el9ap`
`receptor` Red Hat:ansible_automation_platform_inside:2.7::el9	All versions	`0:1.6.7-1.el9ap`
`caddy` Red Hat:hummingbird:1	All versions	`0:2.11.4-0.2.hum1`

Products include Quic-Go Project Quic-Go.

How do I fix CVE-2026-40898?

Upgrade github.com/quic-go/quic-go to 0.59.1 or later.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-40898 being exploited?

There is no known exploitation of CVE-2026-40898 in the wild and no public exploit code.

Sources

Also known as CLEANSTART-2026-BH40537, CLEANSTART-2026-OT08451, DEBIAN-CVE-2026-40898, GHSA-vvgj-x9jq-8cj9, GO-2026-5676, MINI-2487-4724-f3mm and 61 more.