dbcve.org
QuicheApplication · Cloudflare

CVE-2026-12523

HIGH · 7.5 CVSS v3.1 Published 2026-07-14
Fix available
A fix is available. Upgrade to 0.29.3 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click 5 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

quiche's HTTP/3 implementation pre-allocates memory based on declared frame length without requiring the full payload to be sent, allowing attackers to exhaust memory by sending frames with large declared lengths but minimal actual data. Additionally, QPACK decompression limits are not correctly enforced, permitting HEADERS frames to commit more memory than the configured MAX_FIELD_SECTION_SIZE allows.

MitigationUpgrade to quiche version 0.29.3 or later to receive the memory allocation and QPACK limit fixes.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
QuicheApplication
Affected:>= 0.1.0, < 0.29.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify quiche installation
    Locate the quiche library in your environment - check for quiche crates in Rust projects, system libraries, or applications using HTTP/3 via quiche
    Affected if quiche is present and used for HTTP/3 connections
  2. Determine quiche version
    Query the installed quiche version using your package manager, Cargo.toml dependencies, or library version information, then compare to the fixed version 0.29.3
    Affected if installed version is lower than 0.29.3
  3. Verify HTTP/3 is enabled
    Check if your application or service has HTTP/3 / quiche protocol support actively enabled in configuration
    Affected if HTTP/3 via quiche is enabled and accepting connections
  4. Check QPACK settings
    Inspect your server configuration for MAX_FIELD_SECTION_SIZE settings and QPACK decompression limits if exposed via config or logs
    Affected if QPACK limits are not properly enforced or MAX_FIELD_SECTION_SIZE is configured without corresponding memory limits in the quiche library
  5. Monitor memory behavior
    Observe memory allocation patterns when processing HTTP/3 frames - especially HEADERS frames with large declared sizes but small payloads
    Affected if memory grows disproportionately relative to actual frame data received

You are affected if quiche version is below 0.29.3, HTTP/3 is enabled, and your environment processes incoming HTTP/3 connections where attackers could send specially crafted frames

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.29.3 or later
Fixed in 0.29.3
Interim mitigation

Upgrade to quiche version 0.29.3 or later to receive the memory allocation and QPACK limit fixes.

Recommended fix High confidence

quiche 0.29.3 or later

  1. Identify the current quiche version in use by checking project dependencies or build configuration
  2. Upgrade quiche to version 0.29.3 or later by updating the dependency in your package manager (e.g., Cargo.toml for Rust, or relevant build system)
  3. Verify the upgrade was successful by checking the installed quiche version
  4. Rebuild and redeploy the application using the updated quiche library
  5. Test HTTP/3 functionality to ensure normal operation after the upgrade

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Quiche Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing8.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,520
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-12523 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
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