Cowboy HTTP/1.1 Unbounded Buffering of Pipelined Data During Request Handling Enables Memory Exhaustion
Affects Cowboy 2.18.0 and later over HTTP/1.1; HTTP/2 is not affected. The risk grows with handlers that hold requests open, such as long polling with cowboy_loop. No fixed version is listed in the checked facts.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fix or patch referenced
- Who is exposed
- Default setups
Do first: Check every install: default setups are affected.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 40/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Default setups
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
The Cowboy HTTP server for Erlang lets a remote attacker, without logging in, send unlimited data over a single HTTP/1.1 keep-alive connection while a request handler is still running, exhausting memory and potentially driving the Erlang VM out of memory. The extra data is buffered with no size limit, because the parser's limits only apply after the handler returns.
Read the original description
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.
Once a request has been received in full and its handler is still running, cowboy_http:parse/2 in src/cowboy_http.erl appends every further byte that arrives on the keep-alive connection to the connection buffer and returns to the receive loop without parsing it. The socket stays in active mode and no limit applies to this buffer: max_request_line_length, max_headers and the other parser limits only take effect once the handler returns and parsing resumes, and the only timer in this state is idle_timeout (default 60 seconds), which is reset on every received chunk. A client can therefore send an arbitrary amount of data on one connection for as long as the handler runs, and a few connections to an endpoint that holds requests open can drive the Erlang VM into out-of-memory conditions.
This issue affects cowboy: from 2.18.0 onward.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure22/25Default setups, reachable over the network without a login
- Reach10/20Affects Hex packages
- Severity8.2/10CVSS 8.2
- No patch0/5No signal
What would change the score
- Would score about 80 if added to CISA KEV
- Would score about 75 if CISA's SSVC rates exploitation active
What to do
Check every install: default setups are affected.
Apply the patch listed under Evidence.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- cowboyHex
From 2.18.0
- ninenines/cowboy
Version range not reported
- cowboyHex
From 2.18.0
Evidence 4
- Patch
- Repository
- Link
- Link
Corrections
None so far.
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Questions about CVE-2026-115701
Is CVE-2026-115701 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
Data sent after a request, while its handler is still running, is buffered in the connection process without a limit. Memory use can grow until the Erlang VM runs out of memory, which denies service. A few such connections can be enough.Source: cna.erlef.org, cve.org
Which versions are affected by CVE-2026-115701?
cowboy (Hex): from 2.18.0. cowboy (Hex): from 2.18.0.Source: cve.now feed data
Am I affected, and how do I check?
The Hex cowboy package is affected from version 2.18.0 onward, and the issue requires HTTP/1.1, since HTTP/2 connections are not affected. The buffering window grows with how long a handler keeps a request open, as with long polling via cowboy_loop, streamed responses, or slow backend calls. To check, look up the cowboy version pinned in mix.lock or rebar.lock and see whether the endpoints use HTTP/1.1 and long-held handlers.Source: cna.erlef.org, cve.org
How do I fix CVE-2026-115701?
The checked facts name no fixed version, so no upgrade target can be given yet. Watch the advisory for a patched release and move to it when it is published.Source: cna.erlef.org, cve.org