CVE-2026-105270: Unbounded atom creation while parsing SAML messages in esaml allows atom table exhaustion
Allocation of Resources Without Limits or Throttling vulnerability in esamlbinding in dropbox esaml allows an unauthenticated attacker to exhaust the Erlang VM atom table and crash the node via a crafted SAMLResponse.
esamlbinding:decoderesponse/2 parses the decoded SAMLResponse with xmerlscan:string/2, which interns every element name, attribute name, and namespace prefix it reads as a permanent atom. The SAML consume (ACS) and single-logout endpoints call it on unauthenticated requests before any signature check, so one well-formed document with thousands of distinct names mints thousands of atoms while staying inside the 128 KB request body limit. Atoms are never reclaimed and the VM caps the atom table at about one million entries, so a few dozen requests abort the node.
This issue affects esaml: from 0.1.0 onward.
Affected Software
Event History
Frequently Asked Questions
Does an attacker need a valid SAML assertion or signature to trigger the issue?
No. The affected ACS and single-logout endpoints parse SAMLResponse input before performing any signature check, so an unauthenticated attacker can send a crafted, well-formed SAMLResponse.
Are deployments protected by a 128 KB request-body limit?
No. A malicious document can remain within the 128 KB body limit while containing thousands of distinct element names, attribute names, or namespace prefixes that are interned as permanent Erlang atoms.
Which exposed endpoints are relevant for triage?
The SAML consume (ACS) and single-logout endpoints are relevant because they invoke the affected parsing path on unauthenticated requests. Deployments that do not expose these endpoints are not described as reachable through this attack path.
How quickly can this affect node availability?
The Erlang VM atom table is capped at about one million entries and atoms are never reclaimed. The report states that a few dozen crafted requests can exhaust the table and abort the node.