{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/tags/cve-2026-53501/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":[],"_cs_cves":[{"id":"CVE-2026-53502"}],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["Thumbor (\u003c= 7.7.7)"],"_cs_severities":["high"],"_cs_tags":["web-application-vulnerability","hmac-bypass","image-processing","cve-2026-53501","ssrf","web-application","input-validation"],"_cs_type":"advisory","_cs_vendors":["Thumbor"],"content_html":"\u003cp\u003eThumbor, an open-source image processing service, contains a path traversal vulnerability (CVE-2026-53502) in its \u003ccode\u003efile_loader\u003c/code\u003e component. The flaw arises because the application performs security validation - using \u003ccode\u003eabspath()\u003c/code\u003e and \u003ccode\u003estartswith()\u003c/code\u003e - on the file path before calling \u003ccode\u003eunquote()\u003c/code\u003e. Attackers can supply double-percent-encoded traversal sequences, such as \u003ccode\u003e%252e%252e\u003c/code\u003e, which evade the initial security check by being treated as literal directory names. Once the check passes, \u003ccode\u003eunquote()\u003c/code\u003e decodes these sequences into standard traversal characters (\u003ccode\u003e..\u003c/code\u003e), allowing the loader to traverse outside the designated root directory.\u003c/p\u003e\n\u003cp\u003eThis issue specifically impacts configurations where \u003ccode\u003efile_loader\u003c/code\u003e is used and the watermark or frame filters are enabled. An attacker can leverage this to read arbitrary files from the server's filesystem, including sensitive configuration files or keys, and receive the file contents overlaid as an image if the data can be parsed as an image format. This affects Thumbor versions 7.7.7 and below.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAttacker constructs a malicious URL targeting a Thumbor watermark filter endpoint (e.g., \u003ccode\u003e/unsafe/filters:watermark(...)\u003c/code\u003e).\u003c/li\u003e\n\u003cli\u003eAttacker embeds double-encoded path traversal sequences (e.g., \u003ccode\u003e%252e%252e\u003c/code\u003e) into the watermark image path parameter.\u003c/li\u003e\n\u003cli\u003eThe web server (Tornado) decodes the first layer of encoding, passing \u003ccode\u003e%2e%2e\u003c/code\u003e to the application logic.\u003c/li\u003e\n\u003cli\u003eThe \u003ccode\u003efile_loader\u003c/code\u003e receives the path and performs \u003ccode\u003eabspath()\u003c/code\u003e, which treats the literal \u003ccode\u003e%2e%2e\u003c/code\u003e as a directory name, causing the \u003ccode\u003estartswith(ROOT)\u003c/code\u003e security check to return True.\u003c/li\u003e\n\u003cli\u003eThe \u003ccode\u003efile_loader\u003c/code\u003e identifies the path as non-existent (as the literal directory doesn't exist) and proceeds to call \u003ccode\u003eunquote()\u003c/code\u003e.\u003c/li\u003e\n\u003cli\u003eThe \u003ccode\u003eunquote()\u003c/code\u003e function decodes \u003ccode\u003e%2e%2e\u003c/code\u003e into \u003ccode\u003e..\u003c/code\u003e, effectively enabling directory traversal.\u003c/li\u003e\n\u003cli\u003eThe application opens the file requested from the filesystem, traversing outside the \u003ccode\u003eFILE_LOADER_ROOT_PATH\u003c/code\u003e.\u003c/li\u003e\n\u003cli\u003eThe file content is returned to the user, potentially displaying sensitive file data as an image artifact.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eSuccessful exploitation results in unauthorized arbitrary file read on the host server. This allows attackers to access critical system files, application configuration files, and environment secrets, which may lead to further compromise of the underlying infrastructure or exfiltration of sensitive organizational data.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eUpgrade Thumbor to a version that performs URL decoding prior to filesystem path validation.\u003c/li\u003e\n\u003cli\u003eImplement strict ingress filtering on web application firewalls to block double-percent-encoded characters (\u003ccode\u003e%252e\u003c/code\u003e) in query parameters targeting watermark or frame filters.\u003c/li\u003e\n\u003cli\u003eDeploy the Sigma rule below to detect attempts to inject encoded traversal sequences into the application.\u003c/li\u003e\n\u003cli\u003eAudit logs for HTTP 200 responses originating from watermark or frame filter endpoints that involve character strings suggestive of path traversal.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-07-31T19:29:15Z","date_published":"2026-07-31T19:20:49Z","id":"https://feed.craftedsignal.io/briefs/2026-07-thumbor-path-traversal/","summary":"Thumbor version 7.7.7 and earlier is vulnerable to arbitrary file read via a path traversal flaw in file_loader.py, where security checks are performed before decoding percent-encoded traversal sequences.","title":"Thumbor Path Traversal via URL Decoding Bypass","url":"https://feed.craftedsignal.io/briefs/2026-07-thumbor-path-traversal/"}],"language":"en","title":"CraftedSignal Threat Feed - Cve-2026-53501","version":"https://jsonfeed.org/version/1.1"}