Headline
CVE-2023-47627: Problems in HTTP parser (the python one, not llhttp)
aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. The HTTP parser in AIOHTTP has numerous problems with header parsing, which could lead to request smuggling. This parser is only used when AIOHTTP_NO_EXTENSIONS is enabled (or not using a prebuilt wheel). These bugs have been addressed in commit d5c12ba89 which has been included in release version 3.8.6. Users are advised to upgrade. There are no known workarounds for these issues.
Summary
The HTTP parser in AIOHTTP has numerous problems with header parsing, which could lead to request smuggling.
This parser is only used when AIOHTTP_NO_EXTENSIONS is enabled (or not using a prebuilt wheel).
Details****Bug 1: Bad parsing of Content-Length values****Description
RFC 9110 says this:
Content-Length = 1*DIGIT
AIOHTTP does not enforce this rule, presumably because of an incorrect usage of the builtin int constructor. Because the int constructor accepts + and - prefixes, and digit-separating underscores, using int to parse CL values leads AIOHTTP to significant misinterpretation.
Examples
GET / HTTP/1.1\r\n
Content-Length: -0\r\n
\r\n
X
GET / HTTP/1.1\r\n
Content-Length: +0_1\r\n
\r\n
X
Suggested action
Verify that a Content-Length value consists only of ASCII digits before parsing, as the standard requires.
Bug 2: Improper handling of NUL, CR, and LF in header values****Description
RFC 9110 says this:
Field values containing CR, LF, or NUL characters are invalid and dangerous, due to the varying ways that implementations might parse and interpret those characters; a recipient of CR, LF, or NUL within a field value MUST either reject the message or replace each of those characters with SP before further processing or forwarding of that message.
AIOHTTP’s HTTP parser does not enforce this rule, and will happily process header values containing these three forbidden characters without replacing them with SP.
Examples
GET / HTTP/1.1\r\n
Header: v\x00alue\r\n
\r\n
GET / HTTP/1.1\r\n
Header: v\ralue\r\n
\r\n
GET / HTTP/1.1\r\n
Header: v\nalue\r\n
\r\n
Suggested action
Reject all messages with NUL, CR, or LF in a header value. The translation to space thing, while technically allowed, does not seem like a good idea to me.
Bug 3: Improper stripping of whitespace before colon in HTTP headers****Description
RFC 9112 says this:
No whitespace is allowed between the field name and colon. In the past, differences in the handling of such whitespace have led to security vulnerabilities in request routing and response handling. A server MUST reject, with a response status code of 400 (Bad Request), any received request message that contains whitespace between a header field name and colon.
AIOHTTP does not enforce this rule, and will simply strip any whitespace before the colon in an HTTP header.
Example
GET / HTTP/1.1\r\n
Content-Length : 1\r\n
\r\n
X
Suggested action
Reject all messages with whitespace before a colon in a header field, as the standard requires.
PoC
Example requests are embedded in the previous section. To reproduce these bugs, start an AIOHTTP server without llhttp (i.e. AIOHTTP_NO_EXTENSIONS=1) and send the requests given in the previous section. (e.g. by printfing into nc)
Impact
Each of these bugs can be used for request smuggling.
Related news
Red Hat Security Advisory 2024-2010-03 - An update is now available for Red Hat Satellite 6.15. The release contains a new version of Satellite and important security fixes for various components. Issues addressed include HTTP request smuggling, crlf injection, denial of service, file disclosure, and traversal vulnerabilities.
Red Hat Security Advisory 2024-1878-03 - An updated version of Red Hat Update Infrastructure is now available. RHUI 4.8 fixes several security an operational bugs, adds some new features and upgrades the underlying Pulp to a newer version. Issues addressed include HTTP request smuggling, crlf injection, denial of service, and traversal vulnerabilities.
Red Hat Security Advisory 2024-1640-03 - An update is now available for Red Hat Ansible Automation Platform 2.4. Issues addressed include HTTP request smuggling, denial of service, local file inclusion, memory leak, and traversal vulnerabilities.
Red Hat Security Advisory 2024-1057-03 - An update is now available for Red Hat Ansible Automation Platform 2.4. Issues addressed include crlf injection and denial of service vulnerabilities.
# Summary The HTTP parser in AIOHTTP has numerous problems with header parsing, which could lead to request smuggling. This parser is only used when `AIOHTTP_NO_EXTENSIONS` is enabled (or not using a prebuilt wheel). # Details ## Bug 1: Bad parsing of `Content-Length` values ### Description RFC 9110 says this: > `Content-Length = 1*DIGIT` AIOHTTP does not enforce this rule, presumably because of an incorrect usage of the builtin `int` constructor. Because the `int` constructor accepts `+` and `-` prefixes, and digit-separating underscores, using `int` to parse CL values leads AIOHTTP to significant misinterpretation. ### Examples ``` GET / HTTP/1.1\r\n Content-Length: -0\r\n \r\n X ``` ``` GET / HTTP/1.1\r\n Content-Length: +0_1\r\n \r\n X ``` ### Suggested action Verify that a `Content-Length` value consists only of ASCII digits before parsing, as the standard requires. ## Bug 2: Improper handling of NUL, CR, and LF in header values ### Description RFC 9110 says this: > Field ...