# CVE-2026-42792: epmd permanent DoS via EMFILE on accept(2) in erts

Status: published. Published: 2026-07-27. Updated: 2026-11-11.

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 27.3.4.15, OTP 28.5.0.4, and OTP 29.0.4, corresponding to erts from 6.0 before 15.2.7.11, 16.4.0.4, and 17.0.4.

## Remediation

- workaround: * 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. (source: CNA: EEF)
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/erlang/otp/commit/865d203e4a6a8f44179eced9e1428f9259e4a3bb

## Affected products and versions

- Erlang / OTP (otp): ≥ 17.0; < * (affected, otp); unaffected at 27.3.4.15; unaffected at 28.5.0.4; unaffected at 29.0.4. Source: CNA: EEF
- Erlang / OTP (erts): ≥ 6.0; < * (affected, otp); unaffected at 15.2.7.11; unaffected at 16.4.0.4; unaffected at 17.0.4. Source: CNA: EEF
- Erlang / OTP (erlang/otp): ≥ 07b8f441ca711f9812fad9e9115bab3c3aa92f79; < 865d203e4a6a8f44179eced9e1428f9259e4a3bb (affected, git). Source: CNA: EEF

## Severity and prioritization

- CVSS 4.0: 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; source: CNA: EEF

- CISA KEV: No listing in collected sources

- EPSS: 0.43% as of 2026-11-10; percentile 38.14%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-755, CWE-770

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/erlang/otp/security/advisories/GHSA-h6f3-hx58-xhj6 (CNA: EEF; vendor-advisory, related)

- https://cna.erlef.org/cves/CVE-2026-42792.html (CNA: EEF; related)

- https://osv.dev/vulnerability/EEF-CVE-2026-42792 (CNA: EEF; related)

- https://www.erlang.org/doc/system/versions.html#order-of-versions (CNA: EEF; x_version-scheme)

- https://github.com/erlang/otp/commit/07b8f441ca711f9812fad9e9115bab3c3aa92f79 (CNA: EEF; related)

- https://github.com/erlang/otp/commit/865d203e4a6a8f44179eced9e1428f9259e4a3bb (CNA: EEF; patch)

## Provenance

- CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-42792; retrieved 2026-11-11; source updated 2026-11-11

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-42792; retrieved 2026-11-11; source updated Not reported

Revision: 4de9386dee66032eb56bd1533236235f3534f7b4477f4843d9eaaf95fdd5ca1d

Canonical: https://y2.dev/cve/CVE-2026-42792

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