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No exploitation reportedFix available

CVE-2026-27572

Wasmtime can panic when adding excessive fields to a `wasi:http/types.fields` instance

No exploitation reported by the sources we read.

  • Published2026-02-24
  • Fixed in41.0.4 · 40.0.4 · 36.0.6 · 24.0.6
  • WeaknessCWE-770

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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 `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.

Timeline

dates in UTC
  1. 2026-02-2422:16CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-27572?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-27572?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Bytecodealliance wasmtime
BranchAffectedFixed in
41.0≥ 41.0.0, < 41.0.441.0.4
40.0≥ 37.0.0, < 40.0.440.0.4
36.0≥ 25.0.0, < 36.0.636.0.6
24.0< 24.0.624.0.6
24.0≥ 0.0.0-0, < 24.0.624.0.6

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • CVE-2026-27572 Red Hat Product Security1 known affected

    wasmtime: Wasmtime: Denial of Service via excessive HTTP header fields

    rhcl-1/wasm-shim-rhel9 as a component of Red Hat Connectivity Link 1

Full record on NVD

Fix

  1. Update Bytecodealliance wasmtime to 41.0.4 · 40.0.4 · 36.0.6 · 24.0.6
  2. Workaround from the vendor Red Hat Product Security CVE-2026-27572 · 1 productMitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
  3. No fix available, says the vendor Red Hat Product Security CVE-2026-27572 · 1 productAffected

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • CISA-ADPSSVC decisionnone2026-02-27
  • OpenCVESSVC decisionnone—
  • CNACVSS 4.06.9read 2026-10-23
  • NVDCVSS 3.17.5read 2026-10-23
  • CNAweakness (CWE)CWE-770read 2026-10-23
  • FIRST EPSSEPSS score0.7 %2026-10-23
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 4.0 vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Published
2026-02-24
Last Modified
2026-06-17
NVD status
Analyzed

Frequently asked questions

What is CVE-2026-27572?

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 `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.

Is CVE-2026-27572 actively exploited?

Active exploitation of CVE-2026-27572 has not been confirmed. Its EPSS score was 0.7% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-27572?

CVE-2026-27572 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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