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

Description (CNA)

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 (CNA)

Vendor / product	Versions
Erlang / OTP	affected 17.0 before 27.3.4.17; affected 28.0 before 28.5.0.6; affected 29.0 before 29.0.6
Erlang / OTP	affected 5.10 before 9.3.2.7; affected 9.4 before 9.6.2.3; affected 9.7 before 9.7.2
Erlang / OTP	affected d9674f32811cd5bb02b0d6656053b5ee226bc74c before *

CWE

CWE-770

References

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.