Mako is a template library written in Python. Prior to 1.3.12, 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. This vulnerability is fixed in 1.3.12.
PUBLISHED5.2CWE-22
Mako: Path traversal via backslash URI on Windows in TemplateLookup
Problem type
Affected products
sqlalchemy
mako
< 1.3.12 - AFFECTED
References
https://github.com/sqlalchemy/mako/security/advisories/GHSA-2h4p-vjrc-8xpq
https://github.com/sqlalchemy/mako/security/advisories/GHSA-2h4p-vjrc-8xpq
https://github.com/sqlalchemy/mako/issues/435
https://github.com/sqlalchemy/mako/issues/435
https://github.com/sqlalchemy/mako/commit/72e10c573ca0fbcbddd4455abca8ce92a61780d7
https://github.com/sqlalchemy/mako/commit/72e10c573ca0fbcbddd4455abca8ce92a61780d7
https://github.com/sqlalchemy/mako/releases/tag/rel_1_3_12
https://github.com/sqlalchemy/mako/releases/tag/rel_1_3_12
GitHub Security Advisories
GHSA-2h4p-vjrc-8xpq
Mako vulnerable to path traversal via backslash URI on Windows in TemplateLookup
https://github.com/advisories/GHSA-2h4p-vjrc-8xpqSummary
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.
github.com
https://github.com/sqlalchemy/mako/security/advisories/GHSA-2h4p-vjrc-8xpq
github.com
https://github.com/sqlalchemy/mako/issues/435
github.com
https://github.com/sqlalchemy/mako/commit/72e10c573ca0fbcbddd4455abca8ce92a61780d7
github.com
https://github.com/sqlalchemy/mako/releases/tag/rel_1_3_12
nvd.nist.gov
https://nvd.nist.gov/vuln/detail/CVE-2026-44307
github.com
https://github.com/advisories/GHSA-2h4p-vjrc-8xpq
JSON source
https://cveawg.mitre.org/api/cve/CVE-2026-44307Click to expand
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