CVE-2026-65624 (GCVE-0-2026-65624)

Vulnerability from cvelistv5 – Published: 2026-07-28 10:01 – Updated: 2026-07-29 04:17
VLAI
Title
Cowboy HTTP/1.1 max_headers Bypass via Duplicate Header Names Enables Memory Exhaustion
Summary
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.
Severity
6.9 (Medium)
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
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-770 - Allocation of Resources Without Limits or Throttling
Assigner
EEF
References
Impacted products
Vendor Product Version
ninenines cowboy Affected: 2.0.0-pre.4 , < 2.18.0 (semver)
    cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*
 Create a notification for this product.
ninenines cowboy Affected: 309780a9fda145c262a47ac7811ffd50a0271c5b , < 3a34d8c1cfd94326466aa16a9017236691dc9c55 (git)
    cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*
 Create a notification for this product.
Credits
Qiyi Deng / Wuhan University Min Shi / Wuhan University Yongkang Xiao / Wuhan University Jing Chen / Wuhan University Loïc Hoguin Jonatan Männchen / EEF
Show details on NVD website
To clipboard 

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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 (\u003ctt\u003e\\\", \\\"\u003c/tt\u003e for regular headers, \u003ctt\u003e\\\"; \\\"\u003c/tt\u003e for cookies), so the map size stays at one and the \u003ctt\u003emax_headers\u003c/tt\u003e 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 \u003ctt\u003emax_header_name_length\u003c/tt\u003e and \u003ctt\u003emax_header_value_length\u003c/tt\u003e apply), an unauthenticated client can send an arbitrary number of header lines with the same name and grow the connection process\u0027s binary memory to arbitrary size within the request window.\u003c/p\u003e\u003cp\u003eThe impact per connection is bounded by \u003ctt\u003erequest_timeout\u003c/tt\u003e (default 5 seconds, not reset by header data), and by \u003ctt\u003emax_heap_size\u003c/tt\u003e when set (the offending connection process is killed once its heap grows past the limit). When \u003ctt\u003emax_heap_size\u003c/tt\u003e is left at the default (unset), sustained abuse can drive the Erlang VM into out-of-memory conditions.\u003c/p\u003e\u003cp\u003eThis issue affects cowboy from 2.0.0-pre.4 before 2.18.0.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-770\", \"description\": \"CWE-770 Allocation of Resources Without Limits or Throttling\"}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"2.18.0\", \"versionStartIncluding\": \"2.0.0-pre.4\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-07-28T10:01:01.811Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-65624\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-07-28T12:39:27.067Z\", \"dateReserved\": \"2026-07-22T13:55:59.401Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-07-28T10:01:01.811Z\", \"assignerShortName\": \"EEF\"}",
      "dataType": "CVE_RECORD",
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    }
  }
}



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Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.