Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows an unauthenticated remote attacker to exhaust connection process memory over HTTP/1.1.

The HTTP/1.1 handler in cowboyhttp enforces the maxheaders limit by counting the number of distinct header names in a map (maps:size(Headers)). When a request contains multiple header lines with the same name, the values are concatenated into a single ever-growing binary stored under that one map key (", " for regular headers, "; " for cookies), so the map size stays at one and the maxheaders cap (default 100) is never reached. Because no accumulator bounds the total number of header lines or the total byte size of the header block (only per-line maxheadernamelength and maxheadervaluelength apply), an unauthenticated client can send an arbitrary number of header lines with the same name and grow the connection process's binary memory to arbitrary size within the request window.

The impact per connection is bounded by requesttimeout (default 5 seconds, not reset by header data), and by maxheapsize when set (the offending connection process is killed once its heap grows past the limit). When maxheapsize is left at the default (unset), sustained abuse can drive the Erlang VM into out-of-memory conditions.

This issue affects cowboy from 2.0.0-pre.4 before 2.18.0.

Cookie Request Header Injection via Unvalidated Encoder in cowcookie:cookie/1

Unexpected Status Code or Return Value vulnerability in ninenines gun (gunhttp module) allows a malicious HTTP server to force the client into raw protocol mode via an unsolicited 101 Switching Protocols response.

In gunhttp:handleinform/8, when a 101 Switching Protocols response is received over HTTP/1.1, the function verifies only that the Upgrade header is syntactically valid and that the stream reference is a plain reference(). It does not check whether the client ever sent an Upgrade or Connection: upgrade header on the corresponding request. Because this check is absent, any 101 response (solicited or not) causes gun to dispatch a gunupgrade message to the caller and transition the entire connection to raw protocol mode.

A malicious or compromised HTTP server can send an unsolicited 101 response to any HTTP/1.1 request, causing the gun client to abandon HTTP framing for that connection. Once in raw mode, gunraw applies no flow control (flow=infinity) and re-arms socket active mode after every received packet, so the server can flood the client with arbitrary bytes. These are forwarded as unbounded gundata messages to the owner process, exhausting its mailbox and BEAM memory, ultimately crashing the VM.

This issue affects gun: from 2.0.0 before 2.4.0.

gun HTTP/1.1 response buffer has no size limit allowing server-controlled memory exhaustion

Origin Validation Error vulnerability in ninenines gun (gunhttp2 module) allows cross-origin cookie injection via unvalidated HTTP/2 PUSHPROMISE authority.

In gunhttp2:pushpromiseframe/7, the :authority pseudo-header from an incoming PUSHPROMISE frame is stored verbatim into the promised stream record without checking that it matches the connection's origin. When gunhttp2:headersframe/9 later processes the response headers for the promised stream, it calls guncookies:setcookieheader/7 with the unvalidated server-supplied authority before any status branching and before user code can act. This violates RFC 7540 §10.6 / RFC 9113 §8.4, which require receivers to treat as a protocol error any push for a resource the server is not authoritative for.

A malicious or compromised HTTP/2 server can plant cookies scoped to arbitrary third-party domains into the client's shared cookie store. This enables session fixation attacks against those domains and, if the planted cookie overrides a legitimate session token, may result in account takeover. No user interaction beyond making a normal HTTP/2 request to the attacker-controlled server is required.

This issue affects gun: from 2.0.0 before 2.4.0.

HTTP Response Splitting via Non-VCHAR Bytes in cowhttpstructhd:escapestring/2

Unbounded chunk-size hex digits in cowlib cause quadratic CPU and memory DoS

CR Injection in SSE Encoder Enables Event Splitting via cowsse:event/1