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Improper Neutralization of CRLF Sequences ('CRLF Injection')

CVE-2025-57804

Medium
6.9/10

Summary

h2 is a pure-Python implementation of a HTTP/2 protocol stack. Prior to version 4.3.0, an HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls. This issue has been patched in version 4.3.0.

  • LOW
  • NETWORK
  • NONE
  • NONE

CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')

The software uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.

References

Advisory Timeline

  • Published