{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 7.7.7"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "thumbor"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.8.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-53500"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-31T18:36:03Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "## Summary\n\nThe `ALLOWED_SOURCES` configuration is meant to restrict which hosts Thumbor\u0027s HTTP loader may fetch images from. Plain-string entries in that list (the overwhelming majority of real-world and documented configurations) are passed directly to `re.match()` without escaping. Because `.` is a regex wildcard, every dot in a domain name becomes a bypass vector: `s.glbimg.com` silently matches `sXglbimgYcom`, `sAglbimg.com`, and any other hostname that differs only at a dot position. This undermines the primary SSRF defence that `ALLOWED_SOURCES` is intended to provide.\n\n## Affected component\n\n`thumbor/loaders/http_loader.py` \u2014 `validate()`\n\n## Proof of concept\n\n```python\nimport re\nfrom thumbor.config import Config\nfrom thumbor.context import Context\nfrom thumbor.loaders import http_loader as loader\n\nconfig = Config()\nconfig.ALLOWED_SOURCES = [\"s.glbimg.com\"]   # typical user config\nctx = Context(None, config, None)\n\n# These should be blocked \u2014 both return True due to the unescaped dot\nprint(loader.validate(ctx, \"http://sXglbimgYcom/secret.jpg\"))  # True \u2190 bypass\nprint(loader.validate(ctx, \"http://sAglbimg.com/secret.jpg\"))  # True \u2190 bypass\n\n# Legitimate origin \u2014 correctly allowed\nprint(loader.validate(ctx, \"http://s.glbimg.com/logo.jpg\"))    # True \u2190 correct\n```\n\n## Root cause\n\n`thumbor/loaders/http_loader.py` (before fix):\n\n```python\nfor pattern in context.config.ALLOWED_SOURCES:\n    if isinstance(pattern, Pattern):\n        match = url\n    else:\n        pattern = f\"^{pattern}$\"   # \u003c-- dots not escaped, act as regex wildcard\n        match = res.hostname\n\n    if re.match(pattern, match):\n        return True\n```\n\n## Impact\n\nAn attacker who can influence the image source URL passed to Thumbor can fetch images from arbitrary hosts, bypassing the `ALLOWED_SOURCES` allowlist.\n\n**Preconditions:**\n\n- `ALLOWED_SOURCES` contains at least one plain-string entry (the common case; all official documentation examples use plain strings).\n- The attacker can supply or influence the image URL \u2014 true whenever  `ALLOW_UNSAFE_URL = True` (the default), or when the application forwards user input to a signed URL endpoint.\n\n## Fix\n\nApply `re.escape()` to plain-string patterns before compiling them, so every\ncharacter is matched literally:\n\n```python\nelse:\n    pattern = f\"^{re.escape(pattern)}$\"   # dots and other metacharacters are now literal\n    match = res.hostname\n```\n\nThis is a one-call addition with no breaking change for correctly written configurations. Users who need real regular-expression behaviour should supply a compiled pattern (`re.compile(r\"s\\.glbimg\\.com\")`), which is already handled by the existing `isinstance(pattern, Pattern)` branch and is unaffected by this change.\n\nThe `ALLOWED_SOURCES` docstring in `config.py` was also updated to document the two-mode behaviour explicitly.",
  "id": "GHSA-6x26-6r6f-m537",
  "modified": "2026-07-31T18:36:03Z",
  "published": "2026-07-31T18:36:03Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/thumbor/thumbor/security/advisories/GHSA-6x26-6r6f-m537"
    },
    {
      "type": "WEB",
      "url": "https://github.com/thumbor/thumbor/commit/68876715350c6c8f49c324e5515e64908830aed7"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/thumbor/thumbor"
    },
    {
      "type": "WEB",
      "url": "https://github.com/thumbor/thumbor/releases/tag/7.8.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Thumbor treats ALLOWED_SOURCES string patterns as unescaped regex, allowing hostname bypass via wildcard dot"
}