Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 Forwarded Trailers Header Filter Bypass
- Exploited
- No known exploitation
- Fix
- Fixed in 48.0.7, 49.0.4
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 48.0.7, 49.0.4.
- Exploitation0/40No signal
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Data gap: No advisory context yet
- Reach10/20Affects crates.io packages
- Severity6.3/10CVSS 6.3
- No patch0/5No signal
What would change the score
- Would score about 78 if added to CISA KEV
- Would score about 73 if CISA's SSVC rates exploitation active
- Would score about 38 if advisories confirm default setups are exposed
CVE-2026-121440 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.3 (medium) and affects wasmtime; fixed in 48.0.7 and 49.0.4.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- 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? →
- 33/100 · provisional
- Fix
- Fixed in 48.0.7, 49.0.4
- 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
- Exploitation: none
- Automatable: no
- Technical impact: partial
Summary
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 fails to check forwarded trailers against the WasiHttpHooks::is_forbidden_header hook in wasi-http p3. WASIp3 guests can forward a request or response body so its trailers skip embedder-customized forbidden header filtering, undermining header restrictions the embedder intended.
What to do
Upgrade to a fixed version: 48.0.7, 49.0.4.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: partial
- Record last updated
Affected versions
- bytecodealliance wasmtime
From 46.0.0 · fixed in 48.0.7; From 49.0.0 · fixed in 49.0.4
- wasmtime-wasi-httpcrates.io
From 46.0.0 · fixed in 48.0.7; From 49.0.0 · fixed in 49.0.4
Evidence 2
- Advisory
- Link
Corrections
None so far.
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Questions about CVE-2026-121440
Is CVE-2026-121440 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 CVE-2026-121440?
wasmtime: from 46.0.0 before 48.0.7; from 49.0.0 before 49.0.4. wasmtime-wasi-http (crates.io): from 46.0.0 before 48.0.7; from 49.0.0 before 49.0.4.Source: cve.now feed data
How do I fix CVE-2026-121440?
Upgrade to a fixed version: 48.0.7, 49.0.4.Source: cve.now feed data