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Vulnerability · Published Sep 1, 2026 · Assigned by EEF

CVE-2026-70399httpd does not enforce the documented default max_clients connection limit

High 8.7

In plain English

A high-severity resource allocation without limits in OTP from Erlang. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.9% (higher than 61% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)8.7High
Exploit odds (30 days)0.9%top 39.3% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12erlangno fix listedDEBIAN-CVE-2026-70399
Debian:13erlang1:27.3.4.1+dfsg-1+deb13u4DEBIAN-CVE-2026-70399
Debian:14erlang1:29.0.6+dfsg-1DEBIAN-CVE-2026-70399
Ubuntu:22.04:LTSerlang1:24.2.1+dfsg-1ubuntu0.7UBUNTU-CVE-2026-70399
Ubuntu:22.04:LTSerlang1:24.2.1+dfsg-1ubuntu0.7USN-8827-1
Ubuntu:24.04:LTSerlang1:25.3.2.8+dfsg-1ubuntu4.7USN-8827-1
Ubuntu:24.04:LTSerlang1:25.3.2.8+dfsg-1ubuntu4.7UBUNTU-CVE-2026-70399
Ubuntu:26.04:LTSerlang1:27.3.4.6+dfsg-1ubuntu0.1USN-8827-1
Ubuntu:26.04:LTSerlang1:27.3.4.6+dfsg-1ubuntu0.1UBUNTU-CVE-2026-70399

Affected products (as reported)

VendorProductVersions
Erlang OTP 17.0 – before 27.3.4.1728.0 – before 28.5.0.629.0 – before 29.0.6
Erlang OTP 5.10 – before 9.3.2.79.4 – before 9.6.2.39.7 – before 9.7.2
Erlang OTP d9674f32811cd5bb02b0d6656053b5ee226bc74c – before *

Weakness: CWE-770 · Vector: 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

References