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Message-ID: <5afad6dc-911e-4a76-a9fd-e166b9fde5f8@oracle.com> Date: Wed, 3 Apr 2024 13:06:00 -0700 From: Alan Coopersmith <alan.coopersmith@...cle.com> To: oss-security@...ts.openwall.com Subject: CERT/CC VU#421644: HTTP/2 CONTINUATION frames can be utilized for DoS attacks https://kb.cert.org/vuls/id/421644 announces: > HTTP/2 CONTINUATION frames can be utilized for DoS attacks > ========================================================== > > Vulnerability Note VU#421644 > Original Release Date: 2024-04-03 | Last Revised: 2024-04-03 > > Overview > -------- > > HTTP allows messages to include named fields in both header and > trailer sections. These header and trailer fields are serialised as > field blocks in HTTP/2, so that they can be transmitted in multiple > fragments to the target implementation. Many HTTP/2 implementations do > not properly limit or sanitize the amount of CONTINUATION frames sent > within a single stream. An attacker that can send packets to a target > server can send a stream of CONTINUATION frames that will not be > appended to the header list in memory but will still be processed and > decoded by the server or will be appended to the header list, causing > an out of memory (OOM) crash. > > Description > ----------- > > HTTP/2 utilizes header fields within HTTP request and response > messages. Header fields can comprise header lists, which in turn are > broken into header blocks. These header blocks are transmitted in > multiple fragments to the target implementation. HTTP/2 CONTINUATION > frames are used to continue a sequence of field block fragments. They > are utilized in order to split header blocks across multiple > frames. The other two types of header block fragments are HEADERS or > PUSH_PROMISE. CONTINUATION frames can be utilized to continue a header > block fragment that could not be transmitted by the HEADERS or > PUSH_PROMISE frames. A header block is considered completed when the > server receives a set END_HEADERS flag. This is intended to denote > that there are no further CONTINUATION, HEADERS, or PUSH_PROMISE > frames. A vulnerability has been discovered within multiple > implementations that does not limit the amount of CONTINUATION frames > that can be sent within a single stream. > > The implementation will continue to receive frames as long as the > END_HEADERS flag is not set during these communications. An attacker > can initialize a connection to a server with typical HTTP/2 frames and > then receive initial frames from the server. The attacker can then > begin an HTTP request with no set END_HEADERS flags. This can allow an > attacker to send a stream of CONTINUATION frames to the target server, > which can result in an out-of-memory crash, enabling an attacker to > launch a denial of service (DoS) attack against a target server using > a vulnerable implementation. > > Additionally, an attacker can send HPACK Huffman encoded CONTINUATION > frames to a target implementation. This can cause CPU resource > exhaustion and result in a DoS as the the CPU must decode every > encoded frame that it receives. > > Below are several CVE listings to reflect the vulnerability within > different implementations. > > CVE-2024-27983 > > An attacker can make the Node.js HTTP/2 server unavailable by sending > a small amount of HTTP/2 frames packets with a few HTTP/2 frames > inside. It is possible to leave some data in nghttp2 memory after > reset when headers with HTTP/2 CONTINUATION frame are sent to the > server and then a TCP connection is abruptly closed by the client > triggering the Http2Session destructor while header frames are still > being processed (and stored in memory) causing a race condition. > > CVE-2024-27919 > > Envoy's oghttp codec does not reset a request when header map limits > have been exceeded. This allows an attacker to send an sequence of > CONTINUATION frames without the END_HEADERS bit set causing unlimited > memory consumption. > > CVE-2024-2758 > > Tempesta FW rate limits are not enabled by default. They are either > set too large to capture empty CONTINUATION frames attacks or too > small to handle normal HTTP requests appropriately. > > CVE-2024-2653 > > amphp/http will collect HTTP/2 CONTINUATION frames in an unbounded > buffer and will not check the header size limit until it has received > the END_HEADERS flag, resulting in an OOM crash. amphp/http-client and > amphp/http-server are indirectly affected if they're used with an > unpatched version of amphp/http. Early versions of amphp/http-client > with HTTP/2 support (v4.0.0-rc10 to 4.0.0) are also directly affected. > > CVE-2023-45288 > > The Go packages net/http and net/http2 packages do not limit the > number of CONTINUATION frames read for an HTTP/2 request, which > permits an attacker to provide an arbitrarily large set of headers for > a single request, that will be read, decoded, and subsequently > discarded, which may result in excessive CPU consumption. > > CVE-2024-28182 > > An implementation using the nghttp2 library will continue to receive > CONTINUATION frames, and will not callback to the application to allow > visibility into this information before it resets the stream, > resulting in a DoS. > > CVE-2024-27316 > > HTTP/2 CONTINUATION frames without the END_HEADERS flag set can be > sent in a continuous stream by an attacker to an Apache Httpd > implementation, which will not properly terminate the request early. > > CVE-2024-31309 > > HTTP/2 CONTINUATION DoS attack can cause Apache Traffic Server to > consume more resources on the server. Version from 8.0.0 through > 8.1.9, from 9.0.0 through 9.2.3 are affected. > > CVE-2024-30255 > > HTTP/2 protocol stack in Envoy versions 1.29.2 or earlier are > vulnerable to CPU exhaustion due to flood of CONTINUATION > frames. Envoys HTTP/2 codec allows the client to send an unlimited > number of CONTINUATION frames even after exceeding Envoys header map > limits. This allows an attacker to send a sequence of CONTINUATION > frames without the END_HEADERS bit set causing CPU utilization, > consuming approximately 1 core per 300Mbit/s of traffic. > > Impact > ------ > > Successful exploitation of this vulnerability can allow an attacker > the capability to launch DoS attacks against servers utilizing > vulnerable implementations. > > Solution > -------- > > Different HTTP/2 implementations may have separate, unique > vulnerabilities specific to that implementation. It is important to > note that it may be difficult to analyze incoming malicious traffic > exploiting this vulnerability as the HTTP request is not properly > completed. Analysis of raw HTTP traffic may be necessary to determine > an attack utilizing this vulnerability. > > Acknowledgements > ---------------- > > Thank you to Bartek Nowotarski for reporting the vulnerability. > This document was written by Christopher Cullen. https://kb.cert.org/vuls/id/421644 has links to further information from various vendors about how this affects their products. The writeup from the researcher who found & reported this is at https://nowotarski.info/http2-continuation-flood-technical-details/ -- -Alan Coopersmith- alan.coopersmith@...cle.com Oracle Solaris Engineering - https://blogs.oracle.com/solaris
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