CVE-2026-12523: Vulnerability in Cloudflare quiche
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
AI Analysis
Technical Summary
CVE-2026-12523 describes a resource exhaustion vulnerability in Cloudflare quiche's HTTP/3 layer. The vulnerability occurs because quiche pre-allocates memory based on the declared length of certain HTTP/3 frames without requiring the attacker to send the full payload, enabling memory exhaustion. Furthermore, quiche does not correctly enforce QPACK decompression limits, allowing specially crafted HEADERS frames to consume more memory than the MAX_FIELD_SECTION_SIZE setting permits. This can lead to denial of service due to excessive memory consumption. The issue affects quiche version 0.1.0 and was fixed starting with version 0.29.3.
Potential Impact
An attacker can cause a denial of service by exhausting memory resources on systems running vulnerable versions of quiche through crafted HTTP/3 frames. This does not impact confidentiality or integrity but can disrupt availability by causing resource exhaustion.
Mitigation Recommendations
Users should upgrade to quiche version 0.29.3 or later, which contains the fix for this vulnerability. Since quiche is used in Cloudflare's cloud service, the vendor manages remediation for the cloud-hosted service. Check the vendor advisory for confirmation of patch deployment on cloud services.
CVE-2026-12523: Vulnerability in Cloudflare quiche
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
CVSS v3.1
Score 7.5high
Affected software
Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-12523 describes a resource exhaustion vulnerability in Cloudflare quiche's HTTP/3 layer. The vulnerability occurs because quiche pre-allocates memory based on the declared length of certain HTTP/3 frames without requiring the attacker to send the full payload, enabling memory exhaustion. Furthermore, quiche does not correctly enforce QPACK decompression limits, allowing specially crafted HEADERS frames to consume more memory than the MAX_FIELD_SECTION_SIZE setting permits. This can lead to denial of service due to excessive memory consumption. The issue affects quiche version 0.1.0 and was fixed starting with version 0.29.3.
Potential Impact
An attacker can cause a denial of service by exhausting memory resources on systems running vulnerable versions of quiche through crafted HTTP/3 frames. This does not impact confidentiality or integrity but can disrupt availability by causing resource exhaustion.
Mitigation Recommendations
Users should upgrade to quiche version 0.29.3 or later, which contains the fix for this vulnerability. Since quiche is used in Cloudflare's cloud service, the vendor manages remediation for the cloud-hosted service. Check the vendor advisory for confirmation of patch deployment on cloud services.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- cloudflare
- Date Reserved
- 2026-06-17T13:35:37.498Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
- Is Cloud Service
- true
Threat ID: 6a56616e68715ace43d2700f
Added to database: 07/14/2026, 16:18:54 UTC
Last enriched: 07/21/2026, 18:45:58 UTC
Last updated: 08/25/2026, 10:52:07 UTC
Views: 77
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
External Links
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.