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CVE-2026-65624— Cowboy HTTP/1.1 max_headers Bypass via Duplicate Header Names Enables Memory Exhaustion

Quick assessment

Affected
ninenines cowboy
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

ninenines cowboy是ninenines的Web服务器。 ninenines cowboy 2.0.0-pre.4版本至2.18.0之前版本存在资源管理错误漏洞，该漏洞源于cowboy_http模块对HTTP/1.1请求头处理不当，未正确限制相同名称请求头的数量，导致未认证的远程攻击者可发送大量同名请求头耗尽连接进程内存。

CVSS 6.9 · Medium EPSS 0.67% · P50

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 2

VendorProduct Version RangeStatus
ninenines cowboy 2.0.0-pre.4< 2.18.0 affected
309780a9fda145c262a47ac7811ffd50a0271c5b< 3a34d8c1cfd94326466aa16a9017236691dc9c55 affected
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I. Basic Information for CVE-2026-65624

Vulnerability Information
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Vulnerability Title
Cowboy HTTP/1.1 max_headers Bypass via Duplicate Header Names Enables Memory Exhaustion
Source: CVE Program / CVE List V5
Vulnerability 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. The HTTP/1.1 handler in cowboy_http enforces the max_headers 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 max_headers 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 max_header_name_length and max_header_value_length 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 request_timeout (default 5 seconds, not reset by header data), and by max_heap_size when set (the offending connection process is killed once its heap grows past the limit). When max_heap_size 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
不加限制或调节的资源分配
Source: CVE Program / CVE List V5
Vulnerability Title
ninenines cowboy 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
ninenines cowboy是ninenines的Web服务器。 ninenines cowboy 2.0.0-pre.4版本至2.18.0之前版本存在资源管理错误漏洞，该漏洞源于cowboy_http模块对HTTP/1.1请求头处理不当，未正确限制相同名称请求头的数量，导致未认证的远程攻击者可发送大量同名请求头耗尽连接进程内存。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
ninenines cowboy 2.0.0-pre.4 ~ 2.18.0 cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*
ninenines cowboy 309780a9fda145c262a47ac7811ffd50a0271c5b ~ 3a34d8c1cfd94326466aa16a9017236691dc9c55 cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-65624

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III. Intelligence Information for CVE-2026-65624

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Patches & Fixes for CVE-2026-65624 (1)

Vendor Advisories for CVE-2026-65624 (2)

IV. Related Vulnerabilities

Same product: cowboy
Same vendor: ninenines
Same weakness: CWE-770

V. Comments for CVE-2026-65624

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