CVE-2026-43973
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk31th percentile - higher than 31% of all known CVEs
Summary
A vulnerability in the gun_http module of the gun library (Erlang/Elixir) allows a malicious server to exhaust client memory via unbounded HTTP/1.1 response buffering. The handle/5 function accumulates TCP data in the connection's buffer without an upper limit when the expected terminator (e.g., \r\n\r\n) never arrives. A malicious server can send a partial response that never completes, causing continuous buffer growth and memory exhaustion of the BEAM node.
Risk Assessment
The risk involves remote memory exhaustion of a BEAM node by a single malicious connection, potentially leading to node-wide crash.
Recommendation
Upgrade gun to version 2.4.0 or later, which contains the fix.
Other vulnerabilities in gun
See all- CVE-2026-43974High
A vulnerability in the gun_http module of the gun library (Erlang/Elixir) allows a malicious HTTP server to force the client into raw protocol mode via an unsolicited 101 Switching Protocols response. The handle_inform/8 function does not check if the client sent an Upgrade or Connection: upgrade header in the request. After receiving a 101 response, gun switches to raw mode with no flow control, and the server can flood the client with arbitrary data, leading to memory exhaustion and VM crash.
- CVE-2026-43972High
The gun library (gun_http2 module) versions 2.0.0 to 2.4.0 have an origin validation vulnerability. An unvalidated :authority header in PUSH_PROMISE frames allows cookie injection for arbitrary third-party domains, enabling session fixation and account takeover.
Original NVD description (English source)
Uncontrolled Resource Consumption vulnerability in ninenines gun (gun_http module) allows a malicious server to exhaust client memory via unbounded HTTP/1.1 response buffering. In gun_http:handle/5, three clauses accumulate incoming TCP data into the connection's buffer field using binary concatenation with no upper-bound check: the head clause appends data until the \r\n\r\n header terminator is found; the body_chunked clause appends data whenever cow_http_te:stream_chunked/2 returns a more result indicating an incomplete chunk boundary; and the body_trailer clause appends data until the trailing \r\n\r\n is found. In each case, when the expected terminator never arrives, the enlarged binary is stored back into state and the process waits for more data, with no configurable or hard-coded ceiling on buffer size. A malicious or compromised server can exploit this by sending a partial response that never completes. For example, a response may begin with HTTP/1.1 200 OK\r\nX-Pad: followed by an unbounded stream of arbitrary bytes, never sending the header terminator. The gun connection process will continuously append the incoming data to its buffer, causing unbounded heap growth. Because BEAM imposes no per-process heap limit by default, a single malicious connection can exhaust all available memory on the node, causing a node-wide out-of-memory crash. This issue affects gun: from 1.0.0 before 2.4.0.