CVSS 4.0
6.3 mediumCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:NCVE-2026-121440
Medium (6.3). EPSS 0.2% estimated probability of exploitation activity in the next 30 days. Fixed in wasmtime-wasi-http 48.0.7, 49.0.4.
On this page
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.
Severity
CVSS 3.1
3.7 lowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N- EPSS
- 0.2% estimated probability of exploitation activity in the next 30 days; 13th percentile. Scored 2026-11-04. A forecast for this CVE across the internet, not for your own systems.
- CISA's assessment (SSVC)
- Exploitation: none · Automatable: no · Technical impact: partial, assessed 2026-11-03. From CISA's Vulnrichment in the CVE List: whether it is exploited, whether exploiting it can be automated, and how much control it gives.
- CWE
- CWE-424 Improper Protection of Alternate Path
- OWASP Top 10
- A01:2025 Broken Access Control
- Published
- Modified
- Record from
- the NVD, synced
Ask an AI about this CVE
Show the prompt
Explain CVE-2026-121440 for an engineer deciding whether to act. Use https://cve.bz/api/public/cves/CVE-2026-121440?via=ask-ai-copy and https://cve.bz/cve/CVE-2026-121440?via=ask-ai-copy as the source of truth: what is affected and which versions fix it, whether it is in CISA KEV, public exploits, and its EPSS (an internet-wide 30-day estimate of exploitation activity, not a forecast for my systems). If they give no fixed versions, use the CVE record https://cveawg.mitre.org/api/cve/CVE-2026-121440 or the vendor advisory, not third-party mirrors. Tell me how to check whether I am affected and how to verify a fix. Cite the sources and say where they are uncertain.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this CVE's id and public links.
Versions
From the CNA's record in the CVE List.
| Product | Affected |
|---|---|
| bytecodealliance wasmtime | from 46.0.0 before 48.0.7 |
| bytecodealliance wasmtime | from 49.0.0 before 49.0.4 |
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| RUSTSEC-2026-0377 | crates.io | wasmtime-wasi-http | >=46.0.0 <48.0.7 >=49.0.0 <49.0.4 | 48.0.7, 49.0.4 |
Attack patterns (CAPEC)
- CAPEC-127 Directory Indexing Likelihood: High · Severity: Medium
- CAPEC-554 Functionality Bypass Likelihood: Medium · Severity: High
The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits.