Affected versions of the Flask package are vulnerable to Information Disclosure due to missing cache-variation headers when the session object is accessed via certain code paths. In Flask’s session handling, accessing flask.session is intended to set a Vary: Cookie response header, but session key-only access patterns (such as using the Python in operator to test for a key without reading or mutating session values) can bypass the logic that adds the header.

Flask 2.2.5 and 2.3.2 include a fix for CVE-2023-30861: When all of the following conditions are met, a response containing data intended for one client may be cached and subsequently sent by the proxy to other clients. If the proxy also caches 'Set-Cookie' headers, it may send one client's 'session' cookie to other clients. The severity depends on the application's use of the session and the proxy's behavior regarding cookies. The risk depends on all these conditions being met:
1. The application must be hosted behind a caching proxy that does not strip cookies or ignore responses with cookies.
2. The application sets 'session.permanent = True'
3. The application does not access or modify the session at any point during a request.
4. 'SESSION_REFRESH_EACH_REQUEST' enabled (the default).
5. The application does not set a 'Cache-Control' header to indicate that a page is private or should not be cached.
This happens because vulnerable versions of Flask only set the 'Vary: Cookie' header when the session is accessed or modified, not when it is refreshed (re-sent to update the expiration) without being accessed or modified.
https://github.com/pallets/flask/security/advisories/GHSA-m2qf-hxjv-5gpq

Affected versions of the aiohttp package are vulnerable to HTTP Request Smuggling due to the acceptance of duplicate Host headers in incoming HTTP requests. The C extension HTTP parser failed to reject duplicate singleton headers such as Host, Content-Type, and Content-Length, creating parser differentials between the C and pure-Python implementations that could lead to inconsistent request interpretation. An attacker could send a crafted HTTP request containing multiple Host headers to bypass host-based access controls or poison routing decisions in upstream proxies and intermediaries.

Affected versions of the aiohttp package are vulnerable to HTTP Response Splitting due to the default C parser (llhttp) accepting null bytes and control characters in response header values. Specifically, the parser fails to neutralise CRLF sequences and other control characters before including them in outgoing HTTP headers, which means methods such as request.url.origin() may return values that differ from the raw Host header or from what a reverse proxy interpreted. An attacker can craft malicious response headers containing embedded control characters to trigger inconsistent header interpretation, potentially leading to a Security Bypass.

Affected versions of the aiohttp package are vulnerable to HTTP Response Splitting due to improper neutralisation of carriage return characters in the reason phrase of HTTP responses. The Response class does not sanitise the reason parameter, allowing injection of CRLF sequences that can manipulate outgoing HTTP headers. An attacker who controls the reason parameter can inject arbitrary headers into the HTTP response, potentially enabling cache poisoning or response manipulation.

Affected versions of the aiohttp package are vulnerable to Information Disclosure due to improper handling of sensitive headers during cross-origin redirects. When following a redirect to a different origin, the library correctly strips the Authorization header but fails to remove the Cookie and Proxy-Authorization headers, allowing them to be forwarded to the unintended destination. An attacker controlling or observing the redirect target can capture these leaked credentials and session tokens, potentially gaining unauthorised access to user accounts or upstream proxies.

Affected versions of the aiohttp package are vulnerable to Denial of Service due to late enforcement of the client_max_size limit on non-file multipart form fields. When an application uses Request.post() to parse multipart data, the entire field content is read into memory before the size check is applied, allowing oversized payloads to cause significant temporary memory allocation. An attacker can exploit this by sending specially crafted multipart requests to exhaust server memory and degrade service availability.

Affected versions of the aiohttp package are vulnerable to Denial of Service due to insufficient size restrictions on multipart headers. Multipart headers were not subject to the same memory limits enforced for standard HTTP headers, allowing an attacker to send a response containing an excessive number of multipart headers that consume significantly more memory than intended. An attacker could exploit this by crafting a specially formed multipart response to exhaust server memory resources, potentially degrading or disrupting service availability.

Affected versions of the aiohttp package are vulnerable to Server-Side Request Forgery (SSRF) and Information Disclosure due to insufficient path validation in the static resource handler on Windows. The static file serving component fails to properly neutralise UNC path sequences, allowing crafted requests to trigger outbound connections to attacker-controlled SMB servers and leak NTLMv2 credential hashes. An attacker can exploit this by sending a specially crafted request that references a remote UNC path, exposing hashed user credentials and enabling the attacker to read local files on the host system.

Affected versions of the aiohttp package are vulnerable to CRLF Injection due to insufficient sanitization of the content_type parameter during multipart request header construction. An attacker who controls the content_type value passed to a multipart part can embed carriage-return and line-feed characters, allowing arbitrary HTTP headers to be injected into the outgoing request. This can be exploited to manipulate request semantics and perform HTTP Request Splitting when untrusted data is used for the multipart content type.

Affected versions of the aiohttp package are vulnerable to Denial of Service (DoS) due to an unbounded DNS cache in TCPConnector that grows without limit. When an application issues requests to a large number of distinct hosts, the internal DNS resolution cache accumulates entries indefinitely because no maximum size or eviction policy is enforced. An attacker capable of triggering requests to many unique hostnames can cause steadily increasing memory consumption, ultimately degrading or exhausting available resources on the host system.

Affected versions of aiohttp are vulnerable to Uncontrolled Resource Consumption due to insufficient restrictions in header and trailer handling. The vulnerability is in header/trailer handling, where unlimited trailer headers can be processed and cause uncapped memory usage. An attacker can trigger memory exhaustion by sending an attacker-controlled request or response, resulting in reduced availability of the affected service.

Aiohttp 3.8.6 includes a fix for CVE-2023-47627: 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).
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-gfw2-4jvh-wgfg

Affected versions of `aiohttp` are vulnerable to an Improper Validation vulnerability. It is possible for an attacker to modify the HTTP request (e.g. insert a new header) or even create a new HTTP request if the attacker controls the HTTP method. The vulnerability occurs only if the attacker can control the HTTP method (GET, POST etc.) of the request. If the attacker can control the HTTP version of the request it will be able to modify the request (request smuggling).

Affected versions of the aiohttp package are vulnerable to Denial of Service (DoS) due to unbounded decompression of highly compressed HTTP request bodies when the HTTP parser auto_decompress feature is enabled.

Affected versions of the aiohttp package are vulnerable to Denial of Service (DoS) due to excessive warning-level logging when parsing invalid Cookie headers. When server code accesses aiohttp.web_request.Request.cookies, the aiohttp._cookie_helpers.parse_cookie_header() function validates cookie names and can emit a log entry for each illegal cookie name, enabling a single request to generate a large number of warning logs.

Affected versions of the aiohttp package are vulnerable to Denial of Service (DoS) due to improper enforcement of request size limits during multipart form parsing. The aiohttp aiohttp.web_request.Request.post() method in aiohttp/web_request.py iterates over multipart fields but (prior to the fix) resets its running byte counter per part rather than tracking the total size of the entire multipart form, allowing the aggregate payload to grow without being bounded by client_max_size.

Affected versions of the aiohttp package are vulnerable to Information Disclosure due to static-file path normalisation enabling inference of absolute path component existence. In aiohttp, applications that register a static route via aiohttp.web.static() may expose filesystem path information because the static handler’s normalization and response behaviour lets a requester distinguish which absolute path components exist.

The aiohttp versions minor than 3.9. has a vulnerability that affects the Python HTTP parser used in the aiohttp library. It allows for minor differences in allowable character sets, which could lead to robust frame boundary matching of proxies to protect against the injection of additional requests. The vulnerability also allows 
 exceptions during validation that aren't handled consistently with other malformed inputs.

Affected versions of `aiohttp` are vulnerable to an infinite loop condition. This occurs when an attacker sends a specially crafted POST (multipart/form-data) request. Upon processing, the `aiohttp` server enters an infinite loop, preventing it from processing further requests. This results in a denial-of-service (DoS) attack, allowing an attacker to stop the application from serving requests after a single request. Users are advised to upgrade to version 3.9.4 or manually apply a patch to their systems as per the linked GHSA instructions.

Aiohttp 3.8.5 includes a fix for CVE-2023-37276: Sending a crafted HTTP request will cause the server to misinterpret one of the HTTP header values leading to HTTP request smuggling.
https://github.com/aio-libs/aiohttp/commit/9337fb3f2ab2b5f38d7e98a194bde6f7e3d16c40
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-45c4-8wx5-qw6w

Aiohttp 3.7.4 includes a fix for CVE-2021-21330: In aiohttp before version 3.7.4 there is an open redirect vulnerability. A maliciously crafted link to an aiohttp-based web-server could redirect the browser to a different website. It is caused by a bug in the 'aiohttp.web_middlewares.normalize_path_middleware' middleware. A workaround can be to avoid using 'aiohttp.web_middlewares.normalize_path_middleware' in your applications.
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-v6wp-4m6f-gcjg

Aiohttp 3.8.0 adds validation of HTTP header keys and values to prevent header injection.
https://github.com/aio-libs/aiohttp/issues/4818

Aiohttp 3.8.0 includes a fix for CVE-2023-47641: Affected versions of aiohttp have a security vulnerability regarding the inconsistent interpretation of the http protocol. HTTP/1.1 is a persistent protocol, if both Content-Length(CL) and Transfer-Encoding(TE) header values are present it can lead to incorrect interpretation of two entities that parse the HTTP and we can poison other sockets with this incorrect interpretation. A possible Proof-of-Concept (POC) would be a configuration with a reverse proxy(frontend) that accepts both CL and TE headers and aiohttp as backend. As aiohttp parses anything with chunked, we can pass a chunked123 as TE, the frontend entity will ignore this header and will parse Content-Length. The impact of this vulnerability is that it is possible to bypass any proxy rule, poisoning sockets to other users like passing Authentication Headers, also if it is present an Open Redirect an attacker could combine it to redirect random users to another website and log the request.
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-xx9p-xxvh-7g8j

Affected versions of the aiohttp package are vulnerable to Denial of Service (DoS) due to excessive blocking CPU usage when processing a large number of HTTP chunked messages. When an aiohttp server endpoint calls request.read(), the chunked body handling performs costly per-chunk processing that can consume a moderate amount of blocking CPU time (for example, around one second) when the request contains an unusually large number of chunks.

Affected versions of the `aiohttp` package are vulnerable to Cross-site Scripting (XSS) due to improper sanitization of user input on index pages for static file handling. The vulnerability exists because the `show_index` option, when enabled, allows unsanitized user input to be rendered directly into the HTML content of directory listings. An attacker can exploit this vulnerability by crafting a malicious URL that, when accessed, executes arbitrary JavaScript in the context of the user's browser, potentially leading to session hijacking or data theft.

Affected versions of the aiohttp package are vulnerable to Denial of Service (DoS) due to relying on Python assert statements for malformed request handling, which are removed when interpreter optimizations are enabled. The aiohttp.web_request.Request.post() method can trigger an infinite loop in multipart POST body processing because assertions in multipart parsing paths, such as aiohttp.multipart.BodyPartReader.read_chunk() and _read_chunk_from_stream() are bypassed, preventing the code from enforcing an exit condition on invalid EOF and boundary states.

Affected versions of the aiohttp package are vulnerable to Request Smuggling due to Unicode digit matching in the Range header parser. In aiohttp.web_request.BaseRequest.http_range, the Range header is parsed with the regular expression ^bytes=(\d*)-(\d*)$ via re.findall(...) without restricting \d to ASCII, which allows non-ASCII decimal characters to be accepted as valid byte-range values.

Affected versions of the aiohttp package are vulnerable to Request Smuggling due to inconsistent Unicode processing of non-ASCII HTTP header values. In the pure-Python HTTP parser (used when the C extensions are not installed or when AIOHTTP_NO_EXTENSIONS is enabled), aiohttp.http_parser.parse_headers() and helpers such as _is_supported_upgrade() and HttpParser._is_chunked_te() apply .lower() to Upgrade, Transfer-Encoding, and Content-Encoding values without first enforcing ASCII-only input, allowing certain non-ASCII characters to be transformed during case-folding and creating parsing discrepancies.

Aiohttp 3.8.6 updates vendored copy of  'llhttp' to v9.1.3 to include a security fix.
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-pjjw-qhg8-p2p9

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.12.14, the Python parser is vulnerable to a request smuggling vulnerability due to not parsing trailer sections of an HTTP request. If a pure Python version of aiohttp is installed (i.e. without the usual C extensions) or AIOHTTP_NO_EXTENSIONS is enabled, then an attacker may be able to execute a request smuggling attack to bypass certain firewalls or proxy protections. Version 3.12.14 contains a patch for this issue.