PYSEC-2026-2617

Vulnerability from pysec - Published: 2026-07-13 15:15 - Updated: 2026-07-13 16:04
VLAI
Details

Summary

On Windows, a URI using backslash traversal (e.g. \..\..\ secret.txt) bypasses the directory traversal check in Template.__init__ and the posixpath-based normalization in TemplateLookup.get_template(), allowing reads of files outside the configured template directory.

Details

The root cause is a mismatch between posixpath (used for URI normalization in get_template()) and os.path (used for file access via os.path.isfile() and validation via os.path.normpath() in Template.__init__). On Windows, os.path is ntpath, which treats \ as a path separator, while posixpath treats it as a literal character.

The vulnerability chain:

  1. get_template() strips only leading / via re.sub(r"^\/+", "", uri) and normalizes with posixpath — backslash \ is treated as a literal character, so \..\ secret.txt passes through with .. undetected.
  2. Template.__init__() validation uses os.path.normpath() — on Windows this resolves \..\ secret.txt to \secret.txt, which does not start with .., so the startswith("..") check passes.
  3. os.path.isfile() on Windows interprets \ as a path separator, resolving the .. traversal and finding files outside the template directory.

Affected code

  • mako/lookup.py: TemplateLookup.get_template() uses posixpath.normpath/posixpath.join for path construction but os.path.isfile() for existence check
  • mako/template.py: Template.__init__() URI validation uses os.path.normpath() which on Windows resolves backslash traversal to a form that passes the startswith("..") guard

Impact

If an application passes user-controlled template names or include paths to TemplateLookup.get_template(), an attacker on Windows may be able to load and disclose readable files outside the configured template directory. The primary impact is local file disclosure. If the targeted file contains Mako/Python template syntax, it may also be parsed and executed as a template.

Remediation

The fix should normalize backslashes to forward slashes early in the URI processing pipeline, before any path operations, to ensure consistent behavior across platforms.

Severity
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Impacted products
Name purl
mako pkg:pypi/mako
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "mako",
        "purl": "pkg:pypi/mako"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.3.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.1.0",
        "0.1.1",
        "0.1.10",
        "0.1.2",
        "0.1.3",
        "0.1.4",
        "0.1.5",
        "0.1.6",
        "0.1.7",
        "0.1.8",
        "0.1.9",
        "0.2.0",
        "0.2.1",
        "0.2.2",
        "0.2.3",
        "0.2.4",
        "0.2.5",
        "0.3.0",
        "0.3.1",
        "0.3.2",
        "0.3.3",
        "0.3.4",
        "0.3.5",
        "0.3.6",
        "0.4.0",
        "0.4.1",
        "0.4.2",
        "0.5.0",
        "0.6.0",
        "0.6.1",
        "0.6.2",
        "0.7.0",
        "0.7.1",
        "0.7.2",
        "0.7.3",
        "0.8.0",
        "0.8.1",
        "0.9.0",
        "0.9.1",
        "1.0.0",
        "1.0.1",
        "1.0.10",
        "1.0.11",
        "1.0.12",
        "1.0.13",
        "1.0.14",
        "1.0.2",
        "1.0.3",
        "1.0.4",
        "1.0.5",
        "1.0.6",
        "1.0.7",
        "1.0.8",
        "1.0.9",
        "1.1.0",
        "1.1.1",
        "1.1.2",
        "1.1.3",
        "1.1.4",
        "1.1.5",
        "1.1.6",
        "1.2.0",
        "1.2.1",
        "1.2.2",
        "1.2.3",
        "1.2.4",
        "1.3.0",
        "1.3.1",
        "1.3.10",
        "1.3.11",
        "1.3.2",
        "1.3.3",
        "1.3.4",
        "1.3.5",
        "1.3.6",
        "1.3.7",
        "1.3.8",
        "1.3.9"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-44307",
    "GHSA-2h4p-vjrc-8xpq"
  ],
  "details": "## Summary\n\nOn Windows, a URI using backslash traversal (e.g. `\\..\\..\\ secret.txt`) bypasses the directory traversal check in `Template.__init__` and the `posixpath`-based normalization in `TemplateLookup.get_template()`, allowing reads of files outside the configured template directory.\n\n\n## Details\n\nThe root cause is a mismatch between `posixpath` (used for URI normalization in `get_template()`) and `os.path` (used for file access via `os.path.isfile()` and validation via `os.path.normpath()` in `Template.__init__`). On Windows, `os.path` is `ntpath`, which treats `\\` as a path separator, while `posixpath` treats it as a literal character.\n\nThe vulnerability chain:\n\n1. `get_template()` strips only leading `/` via `re.sub(r\"^\\/+\", \"\", uri)` and normalizes with `posixpath` \u2014 backslash `\\` is treated as a literal character, so `\\..\\ secret.txt` passes through with `..` undetected.\n2. `Template.__init__()` validation uses `os.path.normpath()` \u2014 on Windows this resolves `\\..\\ secret.txt` to `\\secret.txt`, which does not start with `..`, so the `startswith(\"..\")` check passes.\n3. `os.path.isfile()` on Windows interprets `\\` as a path separator, resolving the `..` traversal and finding files outside the template directory.\n\n### Affected code\n\n- `mako/lookup.py`: `TemplateLookup.get_template()` uses `posixpath.normpath`/`posixpath.join` for path construction but `os.path.isfile()` for existence check\n- `mako/template.py`: `Template.__init__()` URI validation uses `os.path.normpath()` which on Windows resolves backslash traversal to a form that passes the `startswith(\"..\")` guard\n\n## Impact\n\nIf an application passes user-controlled template names or include paths to `TemplateLookup.get_template()`, an attacker on Windows may be able to load and disclose readable files outside the configured template directory. The primary impact is local file disclosure. If the targeted file contains Mako/Python template syntax, it may also be parsed and executed as a template.\n\n## Remediation\n\nThe fix should normalize backslashes to forward slashes early in the URI processing pipeline, before any path operations, to ensure consistent behavior across platforms.",
  "id": "PYSEC-2026-2617",
  "modified": "2026-07-13T16:04:45.912898Z",
  "published": "2026-07-13T15:15:39.881159Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sqlalchemy/mako/security/advisories/GHSA-2h4p-vjrc-8xpq"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44307"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sqlalchemy/mako/issues/435"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sqlalchemy/mako/commit/72e10c573ca0fbcbddd4455abca8ce92a61780d7"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/sqlalchemy/mako"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sqlalchemy/mako/releases/tag/rel_1_3_12"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/mako"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-2h4p-vjrc-8xpq"
    }
  ],
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Mako vulnerable to path traversal via backslash URI on Windows in TemplateLookup"
}



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