Mako vulnerable to path traversal via backslash URI on Windows in TemplateLookup
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:
get_template()strips only leading/viare.sub(r"^\/+", "", uri)and normalizes withposixpath— backslash\is treated as a literal character, so\..\ secret.txtpasses through with..undetected.Template.__init__()validation usesos.path.normpath()— on Windows this resolves\..\ secret.txtto\secret.txt, which does not start with.., so thestartswith("..")check passes.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()usesposixpath.normpath/posixpath.joinfor path construction butos.path.isfile()for existence checkmako/template.py:Template.__init__()URI validation usesos.path.normpath()which on Windows resolves backslash traversal to a form that passes thestartswith("..")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.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | mako | < 1.3.12 | 1.3.12 |
References
- https://github.com/sqlalchemy/mako/security/advisories/GHSA-2h4p-vjrc-8xpq
- https://nvd.nist.gov/vuln/detail/CVE-2026-44307
- https://github.com/sqlalchemy/mako/issues/435
- https://github.com/sqlalchemy/mako/commit/72e10c573ca0fbcbddd4455abca8ce92a61780d7
- https://github.com/sqlalchemy/mako
- https://github.com/sqlalchemy/mako/releases/tag/rel_1_3_12
- https://pypi.org/project/mako
- https://github.com/advisories/GHSA-2h4p-vjrc-8xpq
- CVSS vector
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- Weakness (CWE)
CWE-22- Platform
- Python (PyPI)
- Package
mako- Disclosed
- 06.05.2026
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-2617 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-2h4p-vjrc-8xpq - CC BY 4.0
Vulnerability history: mako
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 5
- First → latest
- 07.2010 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 3
- Medium 2
Disclosures per year
- 2017: 0
- 2018: 0
- 2019: 0
- 2020: 0
- 2021: 0
- 2022: 1
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 3
earlier: 1
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Mako vulnerable to path traversal via backslash URI on Windows in TemplateLookup this entry
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