Weakness Type (CWE)

CWE-755 — CWE-755 Improper Handling of Exceptional Conditions

CAPEC

CVSS 4.0 Score

6.3

MEDIUM

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Vulnerability description

Improper Handling of Exceptional Conditions vulnerability in Erlang OTP erts (epmd) allows an unauthenticated remote attacker to permanently terminate the Erlang Port Mapper Daemon (epmd) via connection slot exhaustion.

The do_accept function in erts/epmd/src/epmd_srv.c calls epmd_cleanup_exit() when accept(2) returns EMFILE (per-process file descriptor limit reached) or ENFILE (system-wide file descriptor limit reached), rather than treating these as recoverable conditions. An attacker can exhaust epmd's file descriptor slots by holding many TCP connections open while periodically sending a single byte to reset the idle timeout, then causing accept(2) to return EMFILE, which kills the daemon. epmd has no per-source-IP connection cap, making the attack feasible from a single source.

On Debian/Ubuntu default packaging the impact is amplified: the systemd unit inherits a low file descriptor soft limit, and repeated daemon deaths trigger systemd's start-rate-limit, permanently failing both epmd.service and epmd.socket and requiring manual operator intervention to recover.

This issue affects OTP from OTP 17.0 before OTP 29.0.4, OTP 28.5.0.4 and OTP 27.3.4.15.

Affected

pkg:otp/erts

Module Source File Routine
epmd_srv epmd/src/epmd_srv.c do_accept
Status Type Version Changes / Fixed in
affected otp ⓘ 6.0
  • unaffected at 17.0.4
  • unaffected at 16.4.0.4
  • unaffected at 15.2.7.11

pkg:github/erlang/otp

Module Source File Routine
epmd_srv erts/epmd/src/epmd_srv.c do_accept
Status Type Version Changes / Fixed in
affected otp ⓘ 17.0
affected git ⓘ 07b8f441ca < 865d203e4a

Workarounds

  • Restrict epmd to loopback only by adding a systemd socket override: set ListenStream= (empty, to clear), then ListenStream=127.0.0.1:4369 and ListenStream=[::1]:4369 in /etc/systemd/system/epmd.socket.d/override.conf.
  • On systemd-managed systems, raise the file descriptor limit and configure automatic restart by adding LimitNOFILE=65536 and Restart=always with a suitable RestartSec in /etc/systemd/system/epmd.service.d/override.conf.
  • Restrict network access to TCP port 4369 via firewall rules to trusted hosts only.

References

Credits

  • Finder: Ryan Moore
  • Remediation developer: John Högberg

CVE record as JSON:  GET /cves/CVE-2026-42792.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-42792.json