CVE-2026-44433 Quicly is vulnerable to memory exhaustion
An adversarial peer can cause memory exhaustion in Quicly by sending crafted STREAM frames, leading to a Denial of Service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-44433?
CVE-2026-44433 is a medium-severity denial of service vulnerability in h2o quicly, published on 16 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 8b178e6, an adversarial peer could send a STREAM frame carrying just one byte at the largest offset being permitted to obtain additional flow control credit, which under certain circumstances could lead to a Denial of Service. Assuming the application prepares a receive buffer for storing all data that arrive out-of-order, up to the largest offset being received, this behavior could lead to the application allocating large amount of memory with the peer sending only a handful of packets, resulting in memory exhaustion. In addition to the receive buffer allocation strategy, the severity of this vulnerability depends on how the application controls the stream concurrency. In case of the H2O HTTP server, under its default setting, this bug increases the maximum amount of memory allocated per connection by about 4 times. This issue has been fixed by commit 8b178e6.
Which versions are affected by CVE-2026-44433?
It affects 1 product.
Products include H2o Quicly.
How do I fix CVE-2026-44433?
No fix has been published for CVE-2026-44433 yet. Limit exposure of the affected software until one is available.
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-2026-44433 being exploited?
There is no known exploitation of CVE-2026-44433 in the wild and no public exploit code.
Other vulnerabilities in h2o quicly
Sources
Also known as GHSA-f7qr-4p37-9gx9.