CVE-2026-28809
MediumCVSS 5.3Exploitation Probability (EPSS)
Low risk20th percentile - higher than 20% of all known CVEs
Summary
The esaml library (and its forks) has an XXE vulnerability. Before signature verification, esaml parses attacker-controlled SAML messages using xmerl_scan:string/2 without disabling XML entity expansion. On Erlang/OTP before version 27, Xmerl allows entities by default, enabling pre-signature XXE attacks. An attacker can read local files (e.g., Kubernetes secrets) and include their contents in the SAML document.
Risk Assessment
An attacker can read sensitive files from the system, such as Kubernetes secrets, potentially leading to credential leakage and privilege escalation.
Recommendation
Upgrade Erlang/OTP to version 27 or later where XML entities are disabled by default, and apply the esaml patch once available.
Other vulnerabilities in esaml
See all- CVE-2026-93471High
Improper Handling of Highly Compressed Data (Data Amplification) in esaml_binding in dropbox esaml allows an unauthenticated attacker to exhaust server memory and crash the Erlang VM via a crafted compressed SAMLResponse. esaml_binding:decode_response/2 base64-decodes the attacker-supplied SAMLResponse, inflates it with zlib:unzip/1 with no bound on the output, then converts the result to a charlist with binary_to_list/1 before parsing. This runs on the SAML consume (ACS) and single-logout endpoints, which accept unauthenticated requests by design, and it runs before any signature check. A small deflate stream reaches a compression ratio near 1000 to 1, so a request body of tens of kilobytes inflates to hundreds of megabytes and then to several gigabytes of list heap, so a few requests exhaust memory and take the node down. This issue affects esaml: from 0.1.0 onward.
- CVE-2026-86696High
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.
- CVE-2026-105270High
In the esaml library (dropbox), esaml_binding:decode_response/2 parses the decoded SAMLResponse with xmerl_scan:string/2, which interns every element name, attribute name, and namespace prefix as a permanent atom. The ACS and single-logout endpoints call it on unauthenticated requests before any signature check, so one document with thousands of distinct names mints thousands of atoms within the 128 KB body limit. Atoms are never reclaimed and the VM caps the atom table at about one million entries, so a few dozen requests can abort the node.
Original NVD description (English source)
XML External Entity (XXE) vulnerability in esaml (and its forks) allows an attacker to cause the system to read local files and incorporate their contents into processed SAML documents, and potentially perform SSRF via crafted SAML messages. esaml parses attacker-controlled SAML messages using xmerl_scan:string/2 before signature verification without disabling XML entity expansion. On Erlang/OTP versions before 27, Xmerl allows entities by default, enabling pre-signature XXE attacks. An attacker can cause the host to read local files (e.g., Kubernetes-mounted secrets) into the SAML document. If the attacker is not a trusted SAML SP, signature verification will fail and the document is discarded, but file contents may still be exposed through logs or error messages. This issue affects all versions of esaml, including forks by arekinath, handnot2, and dropbox. Users running on Erlang/OTP 27 or later are not affected due to Xmerl defaulting to entities disabled.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS