VDB-430361 · CVE-2026-121439 · Nessus 375611

Bytecode Alliance Wasmtime up to 48.0.6/49.0.3 wasi-http response splitting

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
5.2	$0-$5k	0.34

Summaryinfo

A vulnerability, which was classified as problematic, has been found in Bytecode Alliance Wasmtime up to 48.0.6/49.0.3. This affects an unknown function of the component wasi-http. The manipulation leads to response splitting. This vulnerability is documented as CVE-2026-121439. The attack can be initiated remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Bytecode Alliance Wasmtime up to 48.0.6/49.0.3. It has been rated as problematic. This issue affects an unknown functionality of the component wasi-http. The manipulation with an unknown input leads to a response splitting vulnerability. Using CWE to declare the problem leads to CWE-113. The product receives data from an HTTP agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers. Impacted is integrity. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-121439 since 11/03/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Neither technical details nor an exploit are publicly available.

The vulnerability scanner Nessus provides a plugin with the ID 375611 (Linux Distros Unpatched Vulnerability : CVE-2026-121439), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 48.0.7 or 49.0.4 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (375611). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

Bytecode Alliance

Name

Wasmtime

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 5.3
VulDB Meta Temp Score: 5.2

VulDB Base Score: 5.3
VulDB Temp Score: 5.1
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 5.3
CNA Vector (VulnCheck): 🔒

CVSSv2info

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Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Response splitting
CWE: CWE-113 / CWE-93 / CWE-74
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Nessus ID: 375611
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2026-121439

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Wasmtime 48.0.7/49.0.4

Timelineinfo

11/03/2026 Advisory disclosed
11/03/2026 +0 days CVE reserved
11/03/2026 +0 days VulDB entry created
11/04/2026 +1 days VulDB entry last update

Sourcesinfo

Advisory: github.com
Status: Confirmed

CNA: VulnCheck
CVE: CVE-2026-121439 (🔒)

GCVE (CVE): GCVE-0-2026-121439
GCVE (VulDB): GCVE-100-430361

Entryinfo

Created: 11/03/2026 16:14
Updated: 11/04/2026 03:36
Changes: 11/03/2026 16:14 (76), 11/04/2026 03:36 (2)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.