81 行
6.4 KiB
JSON
81 行
6.4 KiB
JSON
{
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"canonical_id": "caddy--CVE-2026-27590",
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"system_id": "caddy",
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"display_name": "Caddy",
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"category": "servers",
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"advisory_mode": "server",
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"title": "Caddy: Unicode case-folding length expansion causes incorrect split_path index in FastCGI transport",
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"summary": "### Summary\n\nCaddy's FastCGI path splitting logic computes the split index on a lowercased copy of the request path and then uses that byte index to slice the original path. This is unsafe for Unicode because `strings.ToLower()` can change UTF-8 byte length for some characters. As a result, Caddy can derive an incorrect `SCRIPT_NAME`/`SCRIPT_FILENAME` and `PATH_INFO`, potentially causing a request that contains `.php` to execute a different on-disk file than intended (path confusion). In setups where an attacker can control file contents (e.g., upload features), this can lead to unintended PHP execution of non-.php files (potential RCE depending on deployment).\n\n### Details\n\nThe issue is in `github.com/caddyserver/caddy/modules/caddyhttp/fastcgi.Trasnport.splitPos()` (and the subsequent slicing in `buildEnv()`):\n\n```\nlowerPath := strings.ToLower(path)\nidx := strings.Index(lowerPath, strings.ToLower(split))\nreturn idx + len(split)\n```\n\nThe returned index is computed in the byte space of lowerPath, but `buildEnv()` applies it to the original path:\n\n- `docURI = path[:splitPos]`\n- `pathInfo = path[splitPos:]`\n- `scriptName = strings.TrimSuffix(path, fc.pathInfo)`\n- `scriptFilename = caddyhttp.SanitizedPathJoin(fc.documentRoot, fc.scriptName)`\n\nThis assumes `lowerPath` and `path` have identical byte lengths and identical byte offsets, which is not true for some Unicode case mappings. Certain characters expand when lowercased (UTF-8 byte length increases), shifting the computed index. This creates a mismatch where `.php` is found in the lowercased string at an offset that does not correspond to the same position in the original string, causing the split point to land later/earlier than intended.\n\n### PoC\n\nCreate a small Go program that reproduces Caddy's `splitPos()` behavior (compute the `.php` split point on a lowercased path, then use that byte index on the original path):\n\n1. Save this as `poc.go`:\n\n```go\npackage main\n\nimport (\n\t\"fmt\"\n\t\"strings\"\n)\n\nfunc splitPos(path string, split string) int {\n\tlowerPath := strings.ToLower(path)\n\tidx := strings.Index(lowerPath, strings.ToLower(split))\n\tif idx < 0 {\n\t\treturn -1\n\t}\n\treturn idx + len(split)\n}\n\nfunc main() {\n\t// U+023A: \u023a (UTF-8: C8 BA). Lowercase is \u2c65 (UTF-8: E2 B1 A5), longer in bytes.\n\tpath := \"/\u023a\u023a\u023a\u023ashell.php.txt.php\"\n\tsplit := \".php\"\n\n\tpos := splitPos(path, split)\n\n\tfmt.Printf(\"orig bytes=%d\\n\", len(path))\n\tfmt.Printf(\"lower bytes=%d\\n\", len(strings.ToLower(path)))\n\tfmt.Printf(\"splitPos=%d\\n\", pos)\n\n\tfmt.Printf(\"orig[:pos]=%q\\n\", path[:pos])\n\tfmt.Printf(\"orig[pos:]=%q\\n\", path[pos:])\n\n\t// Expected split: right after the first \".php\" in the original string\n\twant := strings.Index(path, split) + len(split)\n\tfmt.Printf(\"expected splitPos=%d\\n\", want)\n\tfmt.Printf(\"expected orig[:]=%q\\n\", path[:want])\n}\n```\n\n2. Run it:\n\n```console\ngo run poc.go\n```\n\nOutput on my side:\n\n```\norig bytes=26\nlower bytes=30\nsplitPos=22\norig[:pos]=\"/\u023a\u023a\u023a\u023ashell.php.txt\"\norig[pos:]=\".php\"\nexpected splitPos=18\nexpected orig[:]=\"/\u023a\u023a\u023a\u023ashell.php\"\n```\n\nExpected split is right after the first `.php` (`/\u023a\u023a\u023a\u023ashell.php`). Instead, the computed split lands later and cuts the original path after `shell.php.txt`, leaving `.php` as the remainder.\n\n### Impact\n\nSecurity boundary bypass/path confusion in script resolution.\nIn typical deployments, `.php` extension boundaries are relied on to decide what is executed by PHP. This bug can cause Caddy/FPM to execute a different file than intended by confusing `SCRIPT_NAME`/`SCRIPT_FILENAME`. If an attacker can place attacker-controlled content into a file that can be resolved as `SCRIPT_FILENAME` (common in web apps with uploads or writable directories), this can lead to unintended PHP execution of non-.php files and potentially remote code execution. Severity depends on deployment and presence of attacker-controlled file writes, but the primitive itself is remotely triggerable via crafted URLs.\n\nThis vulnerability was initially reported to FrankenPHP (https://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38) by @AbdrrahimDahmani. The affected code has been copied/adapted from Caddy, which, according to research, is also affected.\n\nThe patch is a port of the FrankenPHP patch.",
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"published_at": "2026-02-24T20:39:08Z",
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"updated_at": "2026-02-27T19:55:10Z",
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"severity": "medium",
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"cvss_score": 4.0,
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"exploit_status": "unknown",
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"source_confidence": "official",
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"official_source_url": "https://github.com/caddyserver/caddy/security/advisories/GHSA-5r3v-vc8m-m96g",
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"secondary_source_urls": [
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"https://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38",
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"https://nvd.nist.gov/vuln/detail/CVE-2026-27590",
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"https://github.com/caddyserver/caddy",
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"https://github.com/caddyserver/caddy/releases/tag/v2.11.1",
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"https://pkg.go.dev/vuln/GO-2026-4536"
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],
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"aliases": [
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"CVE-2026-27590",
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"GO-2026-4536",
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"GHSA-5r3v-vc8m-m96g"
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],
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"cve_ids": [
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"CVE-2026-27590"
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],
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"ghsa_ids": [
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"GHSA-5r3v-vc8m-m96g"
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],
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"osv_ids": [
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"GHSA-5r3v-vc8m-m96g",
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"GO-2026-4536"
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],
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"affected_versions": [
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"introduced=0, fixed<2.11.1"
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],
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"fixed_versions": [
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"2.11.1"
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],
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"package_name": "github.com/caddyserver/caddy/v2",
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"render_markdown": false,
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"case_path": null,
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"secure_code_topics": [
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"proxy-trust-boundary",
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"request-smuggling-boundary",
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"file-upload-validation",
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"plugin-extension-trust-policy",
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"dependency-upgrade-policy"
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],
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"status": "generated",
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"triage_reasons": [],
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"verification_status": "triage-manual",
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"verification_mode": "synthetic",
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"last_verified_at": null,
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"last_run_id": null,
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"evidence_bundle": null,
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"historical_status": null,
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"latest_status": null,
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"browser_evidence": {
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"required": false,
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"present": false,
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"refs": []
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},
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"repro_profile_id": "proxy-boundary-generic",
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"artifact_mode": "synthetic",
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"blocked_reason": null,
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"metadata": {
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"source_names": [
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"OSV Caddy"
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],
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"source_kinds": [
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"osv-batch"
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],
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"candidate_count": 2
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}
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}
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