# CVE-2026-12708: Unbounded HTTP/3 Datagram flow map growth in tokio-quiche

Status: published. Published: 2026-11-10. Updated: 2026-11-10.

Summary


Cloudflare tokio-quiche was found to contain an uncontrolled resource consumption vulnerability in its HTTP/3 DATAGRAM handling. For every previously unseen flow identifier (quarter stream ID) received in a DATAGRAM frame, tokio-quiche creates and retains new, per-flow state. A remote peer can send DATAGRAMs with many distinct identifiers, causing the per-connection flow map and associated channel state to grow without bound.

Impact


Exploitation can exhaust process memory and cause a denial of service. The vulnerable code is used in both client and server configurations, so either role can be affected by a malicious peer. QUIC DATAGRAM support in tokio-quiche is enabled by default through QuicSettings::enable_dgram; applications can disable it by setting this field to false. The vulnerable HTTP/3 path is reachable only when DATAGRAM support is negotiated with the peer. Core quiche and HTTP/3 deployments without DATAGRAM support are not affected. 






Mitigation


Disable DATAGRAMs in tokio-quiche’s QuicSettings::enable_dgram.






Remediation


Upgrade to tokio-quiche version 0.23.0 or later. The fixed code creates flow state only for valid DATAGRAM-capable request streams, which are bounded by QUIC’s stream limits. To tolerate packet reordering, servers retain early DATAGRAMs in a bounded, expiring buffer, while clients discard DATAGRAMs for unknown flows.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Cloudflare / tokio-quiche: ≥ 0.0.1; ≤ 0.20.1 (affected, semver). Source: CNA: cloudflare

## Severity and prioritization

- CVSS 4.0: 8.7 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N; source: CNA: cloudflare

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-401

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://www.cve.org/CVERecord?id=CVE-2026-12708 (CNA: cloudflare)

- https://github.com/cloudflare/quiche/security/advisories/GHSA-wcm9-jv39-r963 (CNA: cloudflare)

## Provenance

- CNA: cloudflare: https://www.cve.org/CVERecord?id=CVE-2026-12708; retrieved 2026-11-10; source updated 2026-11-10

Revision: 2d905955c749df1af1f89f700b0e114b3426e8f4c5c329236b7378ebc8b8b5d0

Canonical: https://y2.dev/cve/CVE-2026-12708

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