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CVE-2026-121440VulnerabilityPublished

Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 fails to check forwarded trailers against the

Affects wasmtimeSource GCVE Database

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Authoritative record:CVE-2026-121440· Medium 6.3

Not known to be exploited · CVSS 6.3 Medium : upgrade to 49.0.4 or 48.0.7 when convenient.

Data as of 3 Nov 2026, 16:15 UTC

CVSS 4.0 base score
6.3Medium
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (VulnCheck)CVSS 4.06.3
CNA (VulnCheck)CVSS 3.13.7
Patch
Available – fixed in 49.0.4, 48.0.7
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 3 Nov 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 3 Nov 2026.

What to do

Upgrade bytecodealliance/wasmtime to 49.0.4 or 48.0.7.

Affected software

ProductAffectedFixed in
crates.iobytecodealliance/wasmtimepkg:cargo/bytecodealliance/wasmtimeOther threatsAffected
  • >=46.0.0 <48.0.7
  • >=49.0.0 <49.0.4
Fixed in
  • 48.0.7
  • 49.0.4

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in Wasmtime versions 48.0.7 and 49.0.4 and later. Users should upgrade to these or newer versions to ensure that forwarded trailers are properly checked against the forbidden header hook. No additional mitigation steps are indicated.

Description

Wasmtime versions 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 contain a vulnerability where forwarded trailers in HTTP requests or responses are not properly checked against the WasiHttpHooks::is_forbidden_header hook in wasi-http p3. This allows WASIp3 guests to bypass embedder-customized forbidden header filtering, potentially undermining intended header restrictions.

References

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