CVE-2026-70399— httpd does not enforce the documented default max_clients connection limit
Quick assessment
Affected
Erlang OTP
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.
Erlang/OTP 中 inets 组件的 httpd 存在“无限制或无节流地分配资源”的漏洞，允许未经身份验证的远程攻击者通过打开并保持大量连接开放而导致服务中断（DoS）。文档说明 max_clients 选项默认为 150，而 inets 安全加固指南将该限制列为服务中断防御的第一道防线。但是，如果服务器未显式设置该选项，它将会接受无限数量的并发连接。仅建立连接即可触发漏洞，无需发送有效请求，也无需进行身份验证。 技术层面，httpd_manager:handle_new_connection/4 中的连接
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I. Basic Information for CVE-2026-70399
Vulnerability Information
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Vulnerability Title
httpd does not enforce the documented default max_clients connection limit
Source: CVE Program / CVE List V5
Vulnerability Description
Allocation of Resources Without Limits or Throttling vulnerability in Erlang/OTP inets httpd allows an unauthenticated remote attacker to cause denial of service by opening and holding open a large number of connections. The max_clients option is documented to default to 150, and the inets hardening guide presents that limit as the first layer of denial-of-service defence, but a server that does not set it explicitly accepts an unlimited number of simultaneous connections. Establishing the connections is sufficient; no valid request and no authentication are required.
The accept gate in httpd_manager:handle_new_connection/4 reads the option with httpd_util:lookup/2, which returns undefined when the key is absent, rather than the three-argument form carrying the 150 default that the neighbouring get_ustate/2 uses. Erlang term ordering places every integer before every atom, so the Count =< Max guard holds for any connection count and the server never returns {reject, busy}. Each accepted connection occupies a worker process and a socket for as long as it is held, driving the node towards process, memory and file descriptor exhaustion. Servers that set max_clients explicitly are unaffected, because a configured value is applied as intended.
This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2.
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:H/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
Affected Products
II. Public POCs for CVE-2026-70399
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Other References for CVE-2026-70399 (6)
Same Patch Batch · Erlang · 2026-09-01 · 8 CVEs total
| CVE-2026-71380 | 8.7 HIGH | httpd applies no timeout while receiving a request body, parking a worker on a stalled cli |
| CVE-2026-66357 | 8.3 HIGH | inets,httpd:HTTP Request Smuggling via obs-fold Header Continuation |
| CVE-2026-73812 | 8.3 HIGH | inets, httpd: HTTP Request Smuggling via Transfer-Encoding and Content-Length |
| CVE-2026-73276 | 8.3 HIGH | inets, httpd: HTTP Request Smuggling via Whitespace-Before-Colon Header Dropping i |
| CVE-2026-55951 | 8.2 HIGH | httpc memory exhaustion via unbounded response header accumulation |
| CVE-2026-59696 | 6.9 MEDIUM | uri_string does not bound the port component of a URI before integer conversion |
| CVE-2026-71562 | 6.3 MEDIUM | httpc does not bound server-supplied numeric header values before integer conversion |
IV. Related Vulnerabilities
Same product: OTP
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CVE-2026-73812
inets, httpd: HTTP Request Smuggling via Transfer-Encoding a -
CVE-2026-73276
inets, httpd: HTTP Request Smuggling via Whitespace-Before-C -
CVE-2026-66357
inets,httpd:HTTP Request Smuggling via obs-fold Header Conti -
CVE-2026-59696
uri_string does not bound the port component of a URI before -
CVE-2026-55951
httpc memory exhaustion via unbounded response header accumu
Same vendor: Erlang
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CVE-2026-73812
inets, httpd: HTTP Request Smuggling via Transfer-Encoding a -
CVE-2026-73276
inets, httpd: HTTP Request Smuggling via Whitespace-Before-C -
CVE-2026-66357
inets,httpd:HTTP Request Smuggling via obs-fold Header Conti -
CVE-2026-59696
uri_string does not bound the port component of a URI before -
CVE-2026-55951
httpc memory exhaustion via unbounded response header accumu
Same weakness: CWE-770
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CVE-2026-55951
httpc memory exhaustion via unbounded response header accumu -
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V. Comments for CVE-2026-70399
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