proxygen's HTTP/3 codec buffered an incomplete non-DATA frame, such as a control-stream frame, a frame of an unknown or reserved type, or a HEADERS frame, until its entire declared length had arrived, without limiting that length, and re-scanned all buffered data each time more bytes arrived. A remote, unauthenticated HTTP/3 peer could declare a very large frame and deliver it slowly, causing unbounded memory growth and CPU usage that grows quadratically with the number of fragments, leading to denial of service. This issue affects proxygen versions prior to v2026.11.09.00.

proxygen's QPACK decoder enforced its size limit on a string literal in an encoder-stream instruction only after the entire literal had been received. A remote, unauthenticated HTTP/3 peer could send an insert instruction on the QPACK encoder stream that declares an arbitrarily large literal and then keep sending data, causing the decoder to buffer it without bound for the lifetime of the connection and exhaust memory, leading to denial of service. The issue occurs regardless of the advertised QPACK dynamic table capacity, including when the dynamic table is disabled. This issue affects proxygen versions prior to v2026.11.09.00.

In proxygen's HTTP/3 session, when a HEADERS block referenced QPACK dynamic table entries that had not yet been received, header decoding for that stream was paused, but the session continued to read the stream from the QUIC transport. The unread data bypassed the session's ingress buffer limit, returned flow-control credit to the peer, and was re-scanned in full on every read. With QPACK blocked streams enabled (the default), a remote, unauthenticated HTTP/3 peer could send a HEADERS block that references a dynamic table insert it never sends, followed by a continuous stream of data, causing memory growth until the request timed out and CPU usage that grows quadratically, leading to denial of service. This issue affects proxygen versions prior to v2026.11.09.00.

Server Crash and Possible Memory Corruption via Pipelined HTTP/1.1 Requests in Facebook Proxygen

When a remote, unauthenticated HTTP/1.1 client pipelined the start of a second request and then stopped reading, proxygen's coroutine-based HTTP session could free that pipelined stream while resetting the connection's streams on the resulting write timeout, then go on to use it. This can crash the server, leading to denial of service, and may allow memory corruption with further impact. This issue affects proxygen versions prior to v2026.11.09.00.

In proxygen from v2026.04.06.00 until v2026.09.28.00, QuicWtSession::closeSession accesses its member fields after calling the base QuicWtSessionBase::closeSession method. The base method notifies the session handler, which may release the last reference to the session and destroy it.

In proxygen from v2024.10.28.00 until v2026.09.28.00, WebTransportImpl::terminateSessionStreams (WebTransportImpl::destroy in releases before v2025.08.18.00) failed to unregister read callbacks for streams that were no longer open before destroying them. The transport could then invoke a read callback that had been freed.

In proxygen from v2024.10.28.00 until v2026.09.28.00, the HTTPTransaction::onWebTransportUniStream and HTTPTransaction::onWebTransportBidiStream APIs could return stream handles that the stream handler had already freed. HQSession then installed those handles as transport read callbacks, which could lead to use of freed memory.

HTTP/2: Multiple HTTP/2 enabled web servers are vulnerable to a DDoS attack (Rapid Reset Attack)

The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset many streams quickly, as exploited in the wild in August through October 2023.

HTTP/2 Flow‑Control Exploit Causes Unbounded Memory Growth in Proxygen

Proxygen lacked a generalized slow-consumer detection mechanism in its core HTTP session layer. A remote, unauthenticated attacker could exploit HTTP/2 flow-control by setting SETTINGS_INITIAL_WINDOW_SIZE to 0 or withholding WINDOW_UPDATE frames, causing the server to buffer complete response bodies in memory indefinitely for stalled streams. By opening many simultaneous streams requesting large resources while preventing the server from transmitting responses, an attacker could induce unbounded memory growth leading to service degradation, resource exhaustion, or denial of service. Versions v2017.01.16.00 through v2026.07.20.00 are affected.

Sending an HTTP request/response body with greater than 2^31 bytes triggers an infinite loop in proxygen::coro::HTTPQuicCoroSession which blocks the backing event loop and unconditionally appends data to a std::vector per-loop iteration. This issue leads to unbounded memory growth and eventually causes the process to run out of memory.

Proxygen fails to validate that a secondary auth manager is set before dereferencing it. That can cause a denial of service issue when parsing a Certificate/CertificateRequest HTTP2 Frame over a fizz (TLS 1.3) transport. This issue affects Proxygen releases starting from v2018.10.29.00 until the fix in v2018.11.19.00.

A packet of death scenario is possible in mvfst via a specially crafted message during a QUIC session, which causes a crash via a failed assertion. Per QUIC specification, this particular message should be treated as a connection error. This issue affects mvfst versions prior to commit a67083ff4b8dcbb7ee2839da6338032030d712b0 and proxygen versions prior to v2021.03.15.00.

A use-after-free is possible due to an error in lifetime management in the request adaptor when a malicious client invokes request error handling in a specific sequence. This issue affects versions of proxygen prior to v2020.05.18.00.

In the course of decompressing HPACK inside the HTTP2 protocol, an unexpected sequence of header table resize operations can place the header table into a corrupted state, leading to a use-after-free condition and undefined behavior. This issue affects Proxygen from v0.29.0 until v2017.04.03.00.

An out of bounds write is possible via a specially crafted packet in certain configurations of Proxygen due to improper handling of Base64 when parsing malformed binary content in Structured HTTP Headers. This issue affects versions of proxygen prior to v2019.07.22.00.