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 ..
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