---
id: "CVE-2026-86696"
kind: "vulnerability"
aliases: ["CVE-2026-86696"]
title: "esaml: unsigned logout requests can crash Erlang node via atom exhaustion"
severity: "high"
cvss: 8.2
epss: 0.00438
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["elixir", "erlang", "package", "saml", "single-sign-on"]
not_affected_if: ["logout-endpoint-not-exposed", "no-esaml-dependency"]
published_at: "2026-10-22T09:17:16+00:00"
first_seen_at: "2026-10-23T21:57:30+00:00"
updated_at: "2026-10-25T03:03:45+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-86696", "first_seen_at": "2026-10-23T21:57:30+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-86696", "first_seen_at": "2026-10-24T07:15:51+00:00"}]
---

# esaml: unsigned logout requests can crash Erlang node via atom exhaustion

esaml, a SAML service provider library for Erlang, turns each distinct unrecognized status value in an unsigned LogoutResponse into a permanent atom. An unauthenticated attacker can exhaust the Erlang VM atom table and crash the node.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check whether the project depends on esaml (`rebar.lock`, `rebar.config`, or `mix.lock` for Elixir projects) and note the version in use
- Check whether the single-logout endpoint is exposed to the internet, since it accepts unsigned LogoutResponse messages

## Fix

- Upgrade esaml to a version that fixes this issue; the sources do not name the fixed version, so unknown
- Until patched, restrict or rate-limit the single-logout endpoint at the proxy or load balancer

## Timeline

- 2026-10-23T21:57:30+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-86696
- 2026-10-24T07:15:51+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-86696

## From the sources

Allocation of Resources Without Limits or Throttling vulnerability in esaml in dropbox esaml allows an unauthenticated attacker to exhaust the Erlang VM atom table and crash the node via unsigned LogoutResponse messages.

esaml:status_code_map/1 in src/esaml.erl maps any StatusCode value it does not recognize to an atom with list_to_atom/1 on the last colon-separated segment of the URN. esaml_sp:validate_logout_response/2 verifies a signature only when the message carries one, so an unsigned LogoutResponse posted to the single-logout endpoint reaches esaml:decode_logout_response/1 and mints one permanent atom per distinct status value. Atoms are never reclaimed and the VM caps the atom table at about one million entries, so an attacker who posts that many distinct values aborts the node.

This issue affects esaml: from 0.1.0 onward.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_