Critical Flaw in Axios Library Puts Countless Web Apps at Risk of RCE

Executive Summary

A critical vulnerability, CVE-2026-40175, has been disclosed in the widely used Axios npm package, a JavaScript library with millions of weekly downloads. The flaw has been assigned a CVSS score of 10.0, reflecting its maximum severity. It is a Server-Side Request Forgery (SSRF) vulnerability that can be escalated by an unauthenticated, remote attacker to achieve Remote Code Execution (RCE). The release of a public proof-of-concept (PoC) exploit demonstrates a viable attack chain for compromising cloud environments by stealing credentials from metadata services. This represents a severe Supply Chain Attack risk, and all developers using affected versions of Axios must upgrade immediately.

Vulnerability Details

The vulnerability is a complex chain of weaknesses:

1. HTTP Response Splitting: The core issue lies in lib/adapters/http.js, where Axios improperly handles header values. An attacker can provide a header containing carriage return and line feed (CRLF) characters (\r\n). Axios merges this into an outbound HTTP request, allowing the attacker to "split" the response and inject arbitrary content or headers (T1197).

2. Prototype Pollution: The SSRF can be chained with a separate prototype pollution vulnerability in a third-party dependency used by the application. This allows the attacker to modify the prototype of base objects in the JavaScript environment.

3. Gadget Attack Chain: The combination of these flaws creates a "Gadget Attack Chain." An attacker can use the SSRF to make the server send a request to a malicious endpoint. The crafted response from this endpoint then exploits the prototype pollution to execute code or manipulate the application's logic. The public PoC demonstrates using this chain to bypass AWS IMDSv2 protections and exfiltrate sensitive cloud credentials.

Affected Systems

• Axios npm package versions below 1.13.2.

Given that Axios is one of the most popular JavaScript libraries, the number of affected web applications and services is potentially in the millions.

Exploitation Status

A public proof-of-concept (PoC) exploit has been released. While there are no confirmed reports of widespread active exploitation yet, the availability of a PoC dramatically lowers the bar for attackers and makes exploitation imminent.

Impact Assessment

The impact is critical (CVSS 10.0). A successful exploit allows an unauthenticated attacker to:

• Achieve Remote Code Execution: Gain full control over the server-side application.
• Compromise Cloud Environments: Steal cloud infrastructure credentials (e.g., AWS IAM roles) from instance metadata services, leading to a full cloud account takeover.
• Bypass Security Controls: The SSRF can be used to bypass firewalls and make requests to internal services that are not exposed to the internet, allowing attackers to scan and attack the internal network.
• Data Exfiltration: Access and steal sensitive data from databases and other internal systems.

Cyber Observables for Detection

Detection Methods

1. Software Composition Analysis (SCA): Use SCA tools (e.g., Snyk, Dependabot) to scan your projects' dependencies and identify all instances of vulnerable Axios versions.
2. Log Analysis (D3-NTA: Network Traffic Analysis): Analyze application and network logs for the observables listed above. Create alerts for any outbound connections from application servers to cloud metadata endpoints or other suspicious internal IPs.
3. Code Review: Manually review code to identify where user-controllable input is being passed into Axios request headers, as this is a potential exploitation point.

Remediation Steps

1. Update Immediately (D3-SU: Software Update): The only definitive solution is to update the Axios package to version 1.13.2 or later in all your projects. Run npm update axios or yarn upgrade axios and redeploy your applications.
2. Input Validation: As a defense-in-depth measure, always sanitize and validate any user-supplied input that is used to construct HTTP requests, including URLs, headers, and body content. Strip any CRLF characters.
3. Network Egress Filtering (M1037): Implement strict egress filtering rules on application servers to block outbound connections to cloud metadata services and other unnecessary internal or external endpoints. This can mitigate the impact of an SSRF attack.