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CVE-2025-53094: ESPAsyncWebServer Vulnerable to CRLF Injection in AsyncWebHeader.cpp

• Severity: high (CVSS 8.7 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-06-27 · updated 2026-06-17
• Weakness: CWE-93

Description

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.

Affected products

• ESP32Async ESPAsyncWebServer: through 3.7.8

References

• https://github.com/ESP32Async/ESPAsyncWebServer/blob/1095dfd1ecf1a903aede29854232af1b24f089b1/src/AsyncWebHeader.cpp#L6-L32
• https://github.com/ESP32Async/ESPAsyncWebServer/pull/211
• https://github.com/ESP32Async/ESPAsyncWebServer/security/advisories/GHSA-87j8-6f7g-h8wh

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