- Exploited
- No known exploitation
- Fix
- Fixed in 0.5.16, 0.6.3
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 0.5.16, 0.6.3.
- 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? →
- 10/100 · provisional
- 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
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.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure?/25Unknown. No advisory context yet
- Reach10/20Affects crates.io packages
- Severity?/10Unknown. No CVSS score or vendor rating
- No patch0/5No signal
What would change the score
- Would score about 65 if added to CISA KEV
- Would score about 60 if CISA's SSVC rates exploitation active
- Would score about 32 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 0.5.16, 0.6.3.
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 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"}.Timeline
- Advisory published44 days
- Record last updated
Affected versions
- quinn-udpcrates.io
From 0.0.0-0 · fixed in 0.5.16; From 0.6.0 · fixed in 0.6.3
Evidence 4
Other links · 4
- Advisory
- Repository
- Repository
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about RUSTSEC-2026-0538
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: cve.now feed data
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: cve.now feed data
How do I fix RUSTSEC-2026-0538?
Upgrade to a fixed version: 0.5.16, 0.6.3.Source: cve.now feed data