Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 HTTP Response Splitting via wasi-http
- 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.
- Exploitation?/40Exploitation: unknown (data gap). No CISA SSVC exploitation rating yet
- 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
- Severity6.9/10CVSS 6.9
- No patch0/5No signal
What would change the score
- Would score about 79 if added to CISA KEV
- Would score about 74 if CISA's SSVC rates exploitation active
- Would score about 39 if advisories confirm default setups are exposed
CVE-2026-121439 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.9 (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- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean?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? →
- 34/100 · 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
Summary
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 contains a response splitting vulnerability in wasi-http p3 that allows guests to set unvalidated content-length headers. Malicious wasip3 guests can splice an existing body into a new response with an incorrect content-length to perform response splitting or injection attacks.
What to do
Upgrade to a fixed version: 48.0.7, 49.0.4.
Timeline
- CVE published
- First seen by cve.now
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.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-121439
Is CVE-2026-121439 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-2026-121439?
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-2026-121439?
Upgrade to a fixed version: 48.0.7, 49.0.4.Source: cve.now feed data