From bd2ffe0cb4cc2d4cb135bfad6c6ce640fde99305 Mon Sep 17 00:00:00 2001 From: Tadej Magajna Date: Thu, 2 Apr 2026 23:26:21 +0200 Subject: [PATCH] gh-142533: Document CRLF injection vulnerabilities in http.server doc (GH-143395) (cherry picked from commit 617f4cc1c2605b86b4833450253c3599b61d6638) Co-authored-by: Tadej Magajna Co-authored-by: Victor Stinner --- Doc/library/http.server.rst | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/Doc/library/http.server.rst b/Doc/library/http.server.rst index 351500174f6df6..fcb0e9feb6aea5 100644 --- a/Doc/library/http.server.rst +++ b/Doc/library/http.server.rst @@ -247,6 +247,8 @@ provides three different variants: specifying its value. Note that, after the send_header calls are done, :meth:`end_headers` MUST BE called in order to complete the operation. + This method does not reject input containing CRLF sequences. + .. versionchanged:: 3.2 Headers are stored in an internal buffer. @@ -257,6 +259,8 @@ provides three different variants: buffered and sent directly the output stream.If the *message* is not specified, the HTTP message corresponding the response *code* is sent. + This method does not reject *message* containing CRLF sequences. + .. versionadded:: 3.2 .. method:: end_headers() @@ -553,6 +557,11 @@ Security considerations requests, this makes it possible for files outside of the specified directory to be served. +Methods :meth:`BaseHTTPRequestHandler.send_header` and +:meth:`BaseHTTPRequestHandler.send_response_only` assume sanitized input +and does not perform input validation such as checking for the presence of CRLF +sequences. Untrusted input may result in HTTP Header injection attacks. + Earlier versions of Python did not scrub control characters from the log messages emitted to stderr from ``python -m http.server`` or the default :class:`BaseHTTPRequestHandler` ``.log_message``