CVE-2026-8466 Details
Description
Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows denial of service via unbounded buffer accumulation in multipart header parsing. cowboy_req:read_part/3 in src/cowboy_req.erl accumulates incoming request bytes into a Buffer binary with no upper-bound check. When cow_multipart:parse_headers/2 returns more or {more, Buffer2}, the function reads up to Length bytes (default 64 KB) from the request body and recurses with the enlarged buffer. There is no equivalent of the byte_size(Acc) > Length guard present in the sibling function read_part_body/4. An unauthenticated attacker can send a multipart/form-data request whose body never yields a complete header section — for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain \r\n\r\n — and force the server process to accumulate memory linearly with the bytes the protocol layer is willing to deliver. A handful of concurrent such uploads is sufficient to exhaust BEAM memory. This issue affects cowboy from 2.0.0 before 2.15.0.
A denial-of-service vulnerability has been identified in Ninenines Cowboy versions 2.0.0 prior to 2.15.0. This issue arises from unbounded buffer accumulation during the parsing of multipart headers. The vulnerability exists in the function 'cowboy_req:read_part/3', which collects incoming request data into a Buffer binary without any upper limit. When 'cow_multipart:parse_headers/2' indicates more data is available, the function reads up to 64 KB from the request body and continues processing with the expanded buffer. Unlike its counterpart 'read_part_body/4', this function lacks a safeguard to prevent excessive data accumulation. An unauthenticated attacker can exploit this by sending a multipart/form-data request that does not provide a complete header section, such as one that fails to include the specified boundary delimiter or does not properly terminate header lines. This can lead to the server process gradually consuming memory in proportion to the amount of data received, with just a few simultaneous uploads being enough to deplete BEAM memory.
Users can upgrade to Ninenines Cowboy version 2.15.0 or later, where this vulnerability has been fixed.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed May 13, 2026CISA-ADP
Assessed May 13, 2026References to Advisories, Solutions, and Tools
By selecting these links, you will be leaving this site. These are references gathered from the official CVE record and are not endorsed by Volerion.
| URL | Source(s) | Tag(s) |
|---|---|---|
| https://cna.erlef.org/cves/CVE-2026-8466.html | EEF | Advisory |
| https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb | EEF | Source CodeVendor |
| https://osv.dev/vulnerability/EEF-CVE-2026-8466 | EEF | Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-770 | Allocation of Resources Without Limits or Throttling | EEF |
Affected Products
| Product | Versions |
|---|---|
| ninenines cowboy | All versions |
CPE
Remediation
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Change History
3 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | EEF |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 13, 2026 | New CVE Received | EEF |