PT-2026-40763 · Cowboy · Cowboy

Loïc Hoguin + 1 · Published 2026-05-13 · Updated 2026-05-20 · CVE-2026-8466

Positive Technologies (AI Summary)

CVSS v4.0

8.2

High

Base vector

AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Name of the Vulnerable Software and Affected Versions cowboy versions 2.0.0 through 2.14.x

Description An issue in multipart header parsing allows an unauthenticated attacker to cause a denial of service via unbounded buffer accumulation. The function read part() in src/cowboy req.erl accumulates incoming request bytes into a Buffer binary without an upper-bound check. When parse headers() returns more data, the function continues to read and recurse with an enlarged buffer. By sending a multipart/form-data request that never yields a complete header section—such as one missing the boundary delimiter or the `

sequence—an attacker can force the server to accumulate memory linearly, potentially exhausting BEAM memory with a few concurrent uploads. This occurs when an HTTP endpoint callsread part/1,2` to process request bodies.

Recommendations Update to version 2.15.0 or later. As a temporary workaround, restrict access to endpoints that process multipart/form-data request bodies using the read part() function.

Fix

DoS

Allocation of Resources Without Limits

Weakness Enumeration

CWE-770

Related Identifiers

CVE-2026-8466

GHSA-468C-VQ7P-GH64

GHSA-JFC2-Q6QH-G5X8

Affected Products

Cowboy

References · 24

• https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb · Patch
• https://cve.org/CVERecord?id=CVE-2026-8466 · Security Note
• https://ubuntu.com/security/CVE-2026-8466 · Vendor Advisory
• https://osv.dev/vulnerability/EEF-CVE-2026-8466 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-8466 · Security Note
• https://osv.dev/vulnerability/GHSA-468c-vq7p-gh64 · Vendor Advisory
• https://osv.dev/vulnerability/GHSA-jfc2-q6qh-g5x8 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-8468 · Security Note
• https://osv.dev/vulnerability/UBUNTU-CVE-2026-8466 · Vendor Advisory
• https://github.com/ninenines/cowboy · Note
• https://github.com/elixir-plug/plug · Note
• https://github.com/elixir-plug/plug/commit/df812a1527bae9e941965e897308a2b8bbf83a94 · Note
• https://github.com/elixir-plug/plug/commit/2cb7958d33030aa826b0c7404375844d4593d43a · Note
• https://github.com/elixir-plug/plug/security/advisories/GHSA-468c-vq7p-gh64 · Note
• https://github.com/elixir-plug/plug/commit/aa69c5ece99c40ded88b8c6581ecc86664b0b734 · Note