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🛡️ CVE-2026-8466 — cowboy

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-770 NVD
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Unbounded buffer accumulation in multipart header parsing causes denial of service in cowboy

Summary

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.

Configuration

The application must expose an HTTP endpoint that calls cowboy\_req:read\_part/1,2 to process multipart/form-data request bodies. Deployments that do not handle multipart uploads are not affected.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Attack requirements: Present — the target has to be in a particular state for the attack to work.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-8466 is classified as CWE-770: Allocation of Resources Without Limits. Resources are allocated on request with no cap, so a client can exhaust them.

Affected software

CVE-2026-8466 is recorded against 2 packages.

  • cowboy
  • unknown

Timeline and source

Published on 13 May 2026 and last revised on 30 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

nvd.nist.gov (Advisory)
github.com (Web)
cna.erlef.org (Web)
github.com (Package)
osv.dev (Web)

Other advisories for this package

cowboy has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-770: Allocation of Resources Without Limits) in other software:

CVE-2026-8466 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CWE CWE-770
Public Exploit ✅ No
Source NVD
Published 2026-05-13
Updated 2026-08-20
Modified 2026-07-30

Affected Packages

Software From version Fixed in
cowboy — —
unknown — —

Similar Threats

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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