CVE-2026-43971
Description
A flaw was found in ninenines cowlib. This vulnerability, due to improper encoding or escaping of output, allows an attacker to perform Link header directive smuggling. By manipulating the target URI, 'rel' value, or attribute keys in applications that process Link headers through cowlib, a remote attacker can inject malicious directives. This can force victim browsers to establish out-of-band connections to attacker-controlled servers, potentially leading to information disclosure or bypassing security controls.
Statement
A flaw was found in cowlib, an Erlang library for HTTP parsing and manipulation. Due to improper encoding of output in the cow_link:link/1 function, an attacker can perform Link header directive smuggling by injecting special characters in the target URI, rel value, or attribute keys. Applications that process Link headers through cowlib and pass untrusted input to cow_link:link/1 may force victim browsers to establish out-of-band connections to attacker-controlled servers, potentially leading to information disclosure or bypassing security controls. Red Hat products that bundle cowlib are only affected if they call cow_link:link/1 with untrusted input; actual exploitability in RabbitMQ Server has not been verified.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 4.3 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | Required | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | Low | N/A | N/A |
| Availability Impact | None | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Modify Application Data; Execute Unauthorized Code or Commands
An attacker could modify the structure of the message or data being sent to the downstream component. When the wrong encoding is used - even if closely related - the downstream component could decode the data incorrectly and misinterpret the output. This can have security consequences when the provided boundaries between control and data are inadvertently broken, because the resulting data could introduce control characters or special elements that were not sent by the product. The resulting data could then be used to bypass protection mechanisms such as input validation, and enable injection attacks.
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