Unbounded SAML message decompression in esaml allows memory exhaustion

{
  "id": "cf4a2532141e0a9c151359a4a36aedc88136fc05913f77dd7b3be9231398887e",
  "url": "https://osv.dev/vulnerability/EEF-CVE-2026-93471",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Unbounded SAML message decompression in esaml allows memory exhaustion",
    "summary": "## Summary 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. ## Details **1. Input.** The SAML consume (ACS) and single-logout endpoints read the request body and pass the `SAMLResponse` form field to `esaml_binding:decode_response/2`. The attacker's `SAMLEncoding` field selects the clause. Both clauses inflate: the explicit DEFLATE clause, and the default clause, which tries `zlib:unzip/1` inside a `catch` whenever the body is not plain XML. **2. Unbounded inflate.** `decode_response/2` evaluates `binary_to_list(zlib:unzip(base64:decode(SAMLResponse)))`. `zlib:unzip/1` inflates the whole stream in one call with no cap on output size, and `binary_to",
    "evidence": "osv:EEF-CVE-2026-93471",
    "products": [
      {
        "name": {
          "value": "esaml",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": [
          {
            "value": "3.0.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.1.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.2.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.3.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.4.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.5.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.6.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.6.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "3.7.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "4.0.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "4.1.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "4.2.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "4.3.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "4.4.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "4.5.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "4.6.0",
            "evidence": "/affected/0/versions"
          }
        ]
      }
    ],
    "severity": "high",
    "structured": {
      "id": "EEF-CVE-2026-93471",
      "aliases": [
        "CVE-2026-93471",
        "EEF-CVE-2026-93471"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0.1.0"
                }
              ]
            }
          ],
          "package": {
            "name": "esaml",
            "purl": "pkg:hex/esaml",
            "ecosystem": "Hex"
          },
          "versions": [
            "3.0.1",
            "3.1.0",
            "3.2.0",
            "3.3.0",
            "3.4.0",
            "3.5.0",
            "3.6.0",
            "3.6.1",
            "3.7.0",
            "4.0.0",
            "4.1.0",
            "4.2.0",
            "4.3.0",
            "4.4.0",
            "4.5.0",
            "4.6.0"
          ],
          "database_specific": {
            "source": "https://cna.erlef.org/osv/EEF-CVE-2026-93471.json"
          }
        },
        {
          "ranges": [
            {
              "repo": "https://github.com/handnot2/esaml",
              "type": "GIT",
              "events": [
                {
                  "introduced": "deeb84378d5c82153b470e99d24f77c38afca14a"
                }
              ]
            }
          ],
          "versions": [
            "v4.2.0",
            "v3.6.1",
            "v4.1.0",
            "v4.0.0",
            "v3.6.0",
            "v3.5.0",
            "v3.4.0",
            "v3.3.0",
            "v3.2.0",
            "v3.1.0",
            "v3.0.1",
            "v3.0.0",
            "v2.1.0",
            "2.0.0",
            "v1.1",
            "v1.0",
            "v0.1"
          ],
          "database_specific": {
            "source": "https://cna.erlef.org/osv/EEF-CVE-2026-93471.json"
          }
        },
        {
          "ranges": [
            {
              "repo": "https://github.com/arekinath/esaml",
              "type": "GIT",
              "events": [
                {
                  "introduced": "deeb84378d5c82153b470e99d24f77c38afca14a"
                }
              ]
            }
          ],
          "versions": [
            "v1.1",
            "v1.0",
            "v0.1"
          ],
          "database_specific": {
            "source": "https://cna.erlef.org/osv/EEF-CVE-2026-93471.json"
          }
        },
        {
          "ranges": [
            {
              "repo": "https://github.com/dropbox/esaml",
              "type": "GIT",
              "events": [
                {
                  "introduced": "deeb84378d5c82153b470e99d24f77c38afca14a"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://cna.erlef.org/osv/EEF-CVE-2026-93471.json"
          }
        }
      ],
      "modified": "2026-10-22T07:00:03.393965193Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-93471.html",
        "https://github.com/handnot2/esaml/commit/deeb84378d5c82153b470e99d24f77c38afca14a",
        "https://github.com/arekinath/esaml/commit/deeb84378d5c82153b470e99d24f77c38afca14a",
        "https://github.com/dropbox/esaml/commit/deeb84378d5c82153b470e99d24f77c38afca14a",
        "https://hex.pm/packages/esaml"
      ],
      "provider_metadata": {
        "cpe_ids": [
          "cpe:2.3:a:handnot2:esaml:*:*:*:*:*:*:*:*",
          "cpe:2.3:a:arekinath:esaml:*:*:*:*:*:*:*:*",
          "cpe:2.3:a:dropbox:esaml:*:*:*:*:*:*:*:*"
        ],
        "cwe_ids": [
          "CWE-409"
        ],
        "capec_ids": [
          "CAPEC-231"
        ]
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-93471",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 404581,
  "published_at": "2026-10-22T06:59:24.029+00:00"
}