CVE-2026-12523 Resource exhaustion in quiche HTTP/3 and QPACK layers
Attackers can cause memory exhaustion in Cloudflare quiche via crafted HTTP/3 frames, leading to 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-2026-12523?
CVE-2026-12523 is a high-severity denial of service vulnerability in Cloudflare quiche, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Summary
Cloudflare quiche's HTTP/3 layer was discovered to be vulnerable to resource exhaustion (i.e., memory) by means of specially crafted HTTP/3 frames.
Impact
HTTP/3 defines multiple frame types to support HTTP message exchanges and connection management. Each frame has a length and a payload whose length depends on the frame type. quiche was found to be vulnerable when parsing some frame types to pre-allocating memory based on the declared length. An attacker would not need to send the number of declared bytes to trigger this issue.
In addition, quiche was found to not apply QPACK decompression limits correctly. This could allow an attacker to send specially crafted HEADERS frames that would cause more memory commitment than otherwise advertised by MAX_FIELD_SECTION_SIZE (configured by set_max_field_section_size()).
Mitigation:
*
Users are requested to upgrade to quiche 0.29.3 which is the earliest version containing the fix for this issue.
Credits: Disclosed responsibly by Sébastien Féry
Weakness: CWE-400
Which versions are affected by CVE-2026-12523?
It affects 1 product.
Products include Cloudflare Quiche.
How do I fix CVE-2026-12523?
No fix has been published for CVE-2026-12523 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-2026-12523 being exploited?
There is no known exploitation of CVE-2026-12523 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in Cloudflare quiche
- CVE-2025-7054 Infinite loop triggered by connection ID retirement
- CVE-2025-4821 Incorrect congestion window growth by invalid ACK ranges
- CVE-2024-1765 Unlimited resource allocation by QUIC CRYPTO frames flooding in quiche
- CVE-2025-4820 Incorrect congestion window growth by optimistic ACK
- CVE-2023-6193 Unbounded queuing of path validation messages in cloudflare-quiche
Sources
Also known as GHSA-4fgf-9xrr-88gf.