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CVE-2026-93471: Unbounded SAML message decompression in esaml allows memory exhaustion

• Severity: high (CVSS 8.7 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-22 · updated 2026-10-30
• Weakness: CWE-409

Description

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.

Affected products

• dropbox esaml: from 0.1.0

References

• https://cna.erlef.org/cves/CVE-2026-93471.html
• https://github.com/arekinath/esaml/commit/deeb84378d5c82153b470e99d24f77c38afca14a
• https://github.com/dropbox/esaml/commit/deeb84378d5c82153b470e99d24f77c38afca14a
• https://github.com/handnot2/esaml/commit/deeb84378d5c82153b470e99d24f77c38afca14a
• https://osv.dev/vulnerability/EEF-CVE-2026-93471
• https://cna.erlef.org/cves/CVE-2026-93471.html
• https://osv.dev/vulnerability/EEF-CVE-2026-93471

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