CVE-2025-53094 in ESPAsyncWebServer
Summary
by MITRE • 06/27/2025
ESPAsyncWebServer is an asynchronous HTTP and WebSocket server library for ESP32, ESP8266, RP2040 and RP2350. In versions up to and including 3.7.8, a CRLF (Carriage Return Line Feed) injection vulnerability exists in the construction and output of HTTP headers within `AsyncWebHeader.cpp`. Unsanitized input allows attackers to inject CR (`\r`) or LF (`\n`) characters into header names or values, leading to arbitrary header or response manipulation. Manipulation of HTTP headers and responses can enable a wide range of attacks, making the severity of this vulnerability high. A fix is available at pull request 211 and is expected to be part of version 3.7.9.
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Analysis
by VulDB Data Team • 06/28/2025
The vulnerability identified as CVE-2025-53094 affects ESPAsyncWebServer, a widely used asynchronous HTTP and WebSocket server library designed for microcontroller platforms including ESP32, ESP8266, RP2040, and RP2350 devices. This library serves as a critical component in IoT and embedded systems applications where web-based interfaces are required for device configuration and monitoring. The flaw resides within the `AsyncWebHeader.cpp` file where HTTP header construction and output processes occur, creating a pathway for malicious input manipulation that can compromise the integrity of HTTP communications.
The technical implementation of this vulnerability stems from inadequate sanitization of user-provided input during HTTP header generation. Specifically, the library fails to properly escape or validate carriage return (`\r`) and line feed (`\n`) characters that are commonly used to delimit HTTP headers and their values. When attacker-controlled data is processed through the header construction logic without proper input validation, these control characters can be injected into header names or values, enabling what is known as CRLF injection. This vulnerability is classified under CWE-117, which addresses improper output neutralization for logs, and aligns with ATT&CK technique T1190 for Proxy Execution through legitimate system processes.
The operational impact of this vulnerability extends beyond simple header manipulation, creating potential attack vectors that can lead to serious security consequences. Attackers could exploit this weakness to inject malicious headers that might redirect users to phishing sites, manipulate session cookies, or inject malicious content into HTTP responses. The ability to manipulate HTTP headers opens doors for various attacks including HTTP response splitting, cache poisoning, and session hijacking scenarios. In IoT environments where these devices often serve as gateways or control points, such vulnerabilities can provide attackers with unauthorized access to critical systems or enable them to compromise entire network infrastructures.
The mitigation strategy for this vulnerability involves upgrading to version 3.7.9 of ESPAsyncWebServer where the fix has been implemented through pull request 211. This fix addresses the root cause by implementing proper input sanitization and validation of header data, ensuring that control characters are properly escaped or filtered before being incorporated into HTTP headers. Organizations utilizing this library should conduct immediate assessments of their deployed systems to identify any instances running vulnerable versions and implement the necessary updates. Security teams should also consider monitoring for potential exploitation attempts through network traffic analysis, particularly looking for unusual header patterns or injection attempts that might indicate active exploitation of this vulnerability.