CVE-2026-126410
Deferred Deferred - Pending Action

Time-of-Check/Time-of-Use Race in Wasmtime's wasi:sockets UDP Implementation

Publication date: 2026-11-13

Last updated on: 2026-11-13

Assigner: VulnCheck

Description
Wasmtime's wasmtime-wasi crate 48.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 contains a time-of-check/time-of-use race in the wasip3 wasi:sockets udp-socket host implementation that lets guests bypass socket_addr_check send restrictions. A malicious guest can race udp-socket.send against udp-socket.connect to deliver attacker-controlled datagrams to addresses the policy permits only for receiving.

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Meta Information

Published
2026-11-13
Last Modified
2026-11-13
Generated
2026-11-13
AI Q&A
2026-11-13
EPSS Evaluated
N/A
NVD
CVE-2026-126410
EUVD
EUVD-2026-125033

Affected Vendors & Products

Showing 6 associated CPEs
Vendor Product Version / Range
wasmtime wasmtime-wasi to 48.0.8 (exc)
wasmtime wasmtime-wasi to 49.0.5 (exc)
wasmtime wasmtime-wasi to 50.0.1 (exc)
bytecodealliance wasmtime to 48.0.8 (exc)
bytecodealliance wasmtime to 49.0.5 (exc)
bytecodealliance wasmtime to 50.0.1 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-367 The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.

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Executive Summary

This vulnerability is a time-of-check/time-of-use (TOCTOU) race condition in Wasmtime's wasmtime-wasi crate affecting UDP socket operations. A malicious guest can exploit a timing flaw between udp-socket.send and udp-socket.connect to bypass send restrictions. The host checks the peer address before enforcing policy, allowing the guest to change the socket's peer address during the check, sending datagrams to addresses permitted only for receiving.

Detection Guidance

Check if your system uses affected Wasmtime versions (48.0.0-48.0.7, 49.0.0-49.0.4, or 50.0.0). Inspect logs for unusual UDP socket activity or policy bypass attempts. No specific commands are provided in the resources.

Impact Analysis

If you use Wasmtime versions 48.0.0 to 48.0.7, 49.0.0 to 49.0.4, or 50.0.0, a malicious guest could send unauthorized datagrams to addresses restricted by your host's policy. This could lead to data leaks, unauthorized network communication, or policy circumvention. Attackers need low privileges and no user interaction.

Compliance Impact

This vulnerability could impact compliance by allowing unauthorized data transmission, violating data protection policies. GDPR requires strict data handling controls; HIPAA mandates secure communication. Bypassing send restrictions may lead to unauthorized data exfiltration, risking non-compliance with these regulations.

Mitigation Strategies

Upgrade to patched versions: 48.0.8, 49.0.5, or 50.0.1. If upgrading is not possible, disable the wasip3 wasi:sockets UDP API or enforce stricter network policies to block unauthorized UDP traffic.

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