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.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- No fix listed
- Who is exposed
- Not reported
Do first: Workaround: 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.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 31/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
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.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.7/10CVSS 8.7
- No patch5/5No patch listed yet
What would change the score
- Would score about 76 if added to CISA KEV
- Would score about 71 if CISA's SSVC rates exploitation active
- Would score about 36 if advisories confirm default setups are exposed
What to do
Workaround: 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.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
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.
Timeline
- CVE published
- First seen by cve.now
- Record last updated
Affected versions
- Cloudflare tokio-quiche
From 0.0.1 · through 0.20.1
Evidence 3
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Corrections
None so far.
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Questions about CVE-2026-12708
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: cve.now feed data
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: github.com
Which versions are affected by CVE-2026-12708?
tokio-quiche: from 0.0.1 through 0.20.1.Source: cve.now feed data
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: github.com
How do I fix CVE-2026-12708?
Move to tokio-quiche 0.23.0 or later, the earliest version that contains the fix.Source: github.com
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: github.com