Vulnerabilities

Vulnerability · CVE-2026-86696

Unbounded atom creation from unsigned LogoutResponse status codes in esaml allows atom table exhaustion

Published Oct 22, 2026 · catalog updated Oct 22, 2026 · Unbounded atom creation from

Last checked Nov 6, 2026. A connected source was read within the last 7 days.

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No confirmed exploitation is on record for CVE-2026-86696. EPSS is 0.66%. Act only if a listed version of Unbounded atom creation from is installed.

Severity

High8.2

Known exploitation

Not in CISA/VulnCheck KEV

EPSS

0.66%

Remediation

Not established

Affected products

Hex esaml

## Summary Allocation of Resources Without Limits or Throttling vulnerability in in dropbox esaml allows an unauthenticated attacker to exhaust the Erlang VM atom table and crash the node via unsigned messages. in maps any value it does not recognize to an atom with on the last colon-separated segment of the URN. verifies a signature only when the message carries one, so an unsigned posted to the single-logout endpoint reaches 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. ## Details **1. Input.** The single-logout endpoint in reads the request body, decodes the form field with , and passes a document to . **2. No signature required.** looks for a element and verifies it only when one is present. An unsigned document passes through unchanged to , which requires only the and attributes before mapping the value. **3. Interning.** matches six known SAML status URNs to fixed atoms. Any other value starting with falls through to a clause that interns the last colon-separated segment with . The attacker chooses that segment, so each request with a fresh value mints one permanent atom. The VM aborts when the atom table reaches its limit of about one million entries. ## Proof of concept 1. Build an unsigned document with , any , and a whose is a fresh URN such as . 2. Deflate and base64-encode it, and post it to the service provider's single-logout endpoint as the form field with set to the DEFLATE URI. 3. skips signature verification because none is present, maps the status through , and the atom table grows by one entry per distinct token. The endpoint answers with an error, but the atom is never reclaimed. Repeat with fresh tokens until the VM aborts. ## Impact An unauthenticated attacker posts unsigned messages with distinct status code URNs to a service provider's