VulnerabilityPublished 28 Jul 2026

CVE-2026-65624: ninenines cowboy · Unthrottled Resource Allocation

Affects ninenines cowboySource CVE Database V5

Not known to be exploited · CVSS 6.9 Medium : upgrade to 2.18.0 when convenient.

Data as of 27 Oct 2026, 05:11 UTC

CVSS 4.0 base score

6.9Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 32% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.18.0, 3a34d8c1cfd94326466aa16a9017236691dc9c55

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

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

microsoft-security-response-ce

What to do

Upgrade cowboy to 2.18.0; cowboy to 3a34d8c1cfd94326466aa16a9017236691dc9c55.

Affected software

Product	Affected	Fixed in
nineninescowboy	Affected >=2.0.0-pre.4 <2.18.0	Fixed in 2.18.0
nineninescowboy	Affected ≥ 309780a9fda145c262a47ac7811ffd50a0271c5b, < 3a34d8c1cfd94326466aa16a9017236691dc9c55	Fixed in 3a34d8c1cfd94326466aa16a9017236691dc9c55
Hexcowboy`pkg:hex/cowboy`Other threats	Affected >=2.0.0-pre.4 <2.18.0	Fixed in 2.18.0

CPE configurations (1)

cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Users should verify if a fixed version is available beyond 2.18.0 or if configuration options like max_heap_size can be set to limit memory usage per connection. If you cannot patch yet, setting max_heap_size to a reasonable limit may mitigate the impact by killing offending connection processes before exhausting system memory.

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.

Impact

An unauthenticated remote attacker can cause a denial of service by exhausting memory resources on the server running cowboy. This can lead to the Erlang VM running out of memory and potentially crashing or becoming unresponsive. The impact is limited per connection by the request timeout and optionally by max_heap_size if configured. Without max_heap_size set, the server is vulnerable to sustained memory exhaustion attacks.

CWE-770Allocation of Resources Without Limits or Throttling (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #25
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
Requirements
Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
Architecture and Design
Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
Architecture and Design
Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
OWASP ASVS 4.0.3
V8.1.4 (opens in a new tab)
V13.4.1 (opens in a new tab)
V11.1.4 (opens in a new tab)
Attack patterns
XML Ping of the Death (opens in a new tab)
Exponential Data Expansion (opens in a new tab)
Serialized Data Parameter Blowup (opens in a new tab)
Serialized Data with Nested Payloads (opens in a new tab)
Oversized Serialized Data Payloads (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

CPE configurations (1)

Description

AI analysisMachine-generated, updated 6 Aug 2026, 19:42 UTC

WeaknessesCWE-770

Technical details

References

Community reviews

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