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CVE-2026-44307

Mako: Path traversal via backslash URI on Windows in TemplateLookup

8.7 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

0.74%Up 0.5 points since May 13, 2026
90%50%10%1%

What each source reports

CVE List Score used 8.7

Mako: Path traversal via backslash URI on Windows in TemplateLookup

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.

Record
CVE-2026-44307
CVSS 4.0
8.7 HighCVSS: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-22
Updated
2026-11-02
EUVDEUVD-2026-29867 8.7

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.

Record
EUVD-2026-29867
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-2h4p-vjrc-8xpq 8.7

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:

  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.

Record
GHSA-2h4p-vjrc-8xpq
CVSS 4.0
8.7 HighCVSS: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-22
Updated
2026-11-02
NVD 8.7

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.

Record
CVE-2026-44307
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Weakness
CWE-22
Updated
2026-11-02
OSV 8.7

Mako: Path traversal via backslash URI on Windows in TemplateLookup

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.

Record
CVE-2026-44307
CVSS 4.0
8.7 HighCVSS: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-22
Updated
2026-11-02
OSVGHSA-2h4p-vjrc-8xpq 8.7

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:

  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.

Record
GHSA-2h4p-vjrc-8xpq
CVSS 4.0
8.7 HighCVSS: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-22
Updated
2026-11-02
OSVPYSEC-2026-2617 8.7

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:

  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.

Record
PYSEC-2026-2617
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Updated
2026-11-02
OSVUBUNTU-CVE-2026-44307 8.7

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.

Record
UBUNTU-CVE-2026-44307
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Updated
2026-11-02
OSVROOT-APP-PYPI-CVE-2026-44307 No score

CVE-2026-44307 in mako - Patched by Root

Root has patched CVE-2026-44307 in the mako package for Root:PyPI. Multiple fixed versions available.

Record
ROOT-APP-PYPI-CVE-2026-44307
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
mako
PyPI
 through 1.3.11
1.3.12
mako
PyPI
 before 1.3.12, plus listed versions
0.1.00.1.10.1.100.1.20.1.3
Show 45 moreShow less
0.1.40.1.50.1.60.1.70.1.80.1.90.2.00.2.10.2.20.2.30.2.40.2.50.3.00.3.10.3.20.3.30.3.40.3.50.3.60.4.00.4.10.4.20.5.00.6.00.6.10.6.20.7.00.7.10.7.20.7.30.8.00.8.10.9.00.9.11.0.01.0.11.0.101.0.111.0.121.0.131.0.141.0.21.0.31.0.41.0.5
1.3.12
mako
Root:PyPI
 before 1.2.4+aikido.1
1.2.4+aikido.1

History

History
RecordedChangedSources
affected
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-44307 is a high vulnerability (CVSS 8.7) in Sqlalchemy Mako, published May 6, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.74%, the 54th percentile. Fixed in mako 1.3.12.

References

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