CVE-2026-27572
Published: 24 February 2026
Summary
CVE-2026-27572 is a medium-severity Allocation of Resources Without Limits or Throttling (CWE-770) vulnerability in Bytecodealliance Wasmtime. Its CVSS base score is 6.9 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 9.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SI-11 (Error Handling).
Deeper analysis
CVE-2026-27572 affects Wasmtime, a runtime for WebAssembly, specifically its implementation of the `wasi:http/types.fields` resource in the `wasmtime-wasi-http` crate. Prior to versions 24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0, the component is susceptible to panics when too many fields are added to the set of headers. This stems from an underlying data structure that panics upon reaching excessive capacity, without graceful handling in Wasmtime. Such panics in a WASI implementation are considered a security vulnerability due to their potential impact on embedders.
The vulnerability can be exploited remotely by unauthenticated attackers (AV:N/AC:L/PR:N) who can execute WebAssembly guest code interacting with the affected WASI HTTP types. By adding an excessive number of header fields, attackers trigger a panic, resulting in a denial-of-service (DoS) condition for the embedder hosting the Wasmtime runtime. The CVSS v3.1 base score of 7.5 reflects high availability impact (A:H) with no confidentiality or integrity effects (C:N/I:N).
Patched versions of Wasmtime (24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0) address the issue by returning a trap to the guest instead of panicking. There are no known workarounds, and embedders are advised to update to a patched release. Related documentation highlights limitations in the underlying http crate's header handling, with fixes detailed in the patching commit and release notes.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8569
Vulnerability details
Wasmtime is a runtime for WebAssembly. Prior to versions 24.0.6, 36.0.6, 4.0.04, 41.0.4, and 42.0.0, Wasmtime's implementation of the `wasi:http/types.fields` resource is susceptible to panics when too many fields are added to the set of headers. Wasmtime's implementation in the…
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`wasmtime-wasi-http` crate is backed by a data structure which panics when it reaches excessive capacity and this condition was not handled gracefully in Wasmtime. Panicking in a WASI implementation is a Denial of Service vector for embedders and is treated as a security vulnerability in Wasmtime. Wasmtime 24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0 patch this vulnerability and return a trap to the guest instead of panicking. There are no known workarounds at this time. Embedders are encouraged to update to a patched version of Wasmtime.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CVE directly enables T1499.004 via remote exploitation of the Wasmtime WASI HTTP types implementation (excessive header fields causing host panic) to achieve application/system DoS.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Requires timely remediation of the Wasmtime flaw causing panic on excessive HTTP header fields, directly enabling update to patched versions that return traps instead.
Mandates secure error handling to prevent panics in the WASI HTTP implementation when data structures exceed capacity, aligning with the patch's graceful trap response.
Protects against the denial-of-service impact from WebAssembly guest-triggered panics due to excessive header fields in Wasmtime.