# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Jul 2026
- **Updated:** 15 Jul 2026
- **Also known as:** GHSA-4fgf-9xrr-88gf

## 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 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-12523?

It affects 1 product.


Products: 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.

## 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:

- CVE-2025-64702, CVE-2026-12523, CVE-2025-13945 (github_poc): https://github.com/HORKimhab/CVE-2025-64702-more

## Other vulnerabilities in Cloudflare quiche

- [CVE-2025-7054](https://insights.sbomify.com/CVE-2025-7054/): Infinite loop triggered by connection ID retirement (high 8.7)
- [CVE-2025-4821](https://insights.sbomify.com/CVE-2025-4821/): Incorrect congestion window growth by invalid ACK ranges (high 7.5)
- [CVE-2024-1765](https://insights.sbomify.com/CVE-2024-1765/): Unlimited resource allocation by QUIC CRYPTO frames flooding in quiche (medium 5.9)
- [CVE-2025-4820](https://insights.sbomify.com/CVE-2025-4820/): Incorrect congestion window growth by optimistic ACK (medium 5.3)
- [CVE-2023-6193](https://insights.sbomify.com/CVE-2023-6193/): Unbounded queuing of path validation messages in cloudflare-quiche (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12523 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-12523 in the wild and no public exploit code.

Affected product: Cloudflare quiche. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-12523/ (Markdown: https://insights.sbomify.com/CVE-2026-12523/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12523
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12523
- OSV: https://osv.dev/vulnerability/CVE-2026-12523

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-12523/
Summaries are generated and may contain mistakes; the official description above is the record.