high CVSS 7.5

CVE-2026-41205·Python vulnerability

Mako is a template library written in Python. Prior to 1.3.11, TemplateLookup.get_template() is vulnerable to path traversal when a URI starts with // (e.g., //../../../secret.txt). The root cause is an inconsistency between two slash-stripping implementations. Any file readable by the process can be returned as rendered template content when an application passes untrusted input directly to TemplateLookup.get_template(). This vulnerability is fixed in 1.3.11.

Severity
high
Software
Python
Fixed in
1.3.11
Published
2026-04-23

Affected versions

Until: 1.3.11

Fixed in: 1.3.11

How to fix this CVE

Update the Mako template library to version 1.3.11 or later to patch a path traversal vulnerability in TemplateLookup.get_template(). This flaw allows attackers to read arbitrary files on the system when untrusted input is passed directly to the template lookup function. Immediately audit your applications to ensure they do not expose user-controlled template paths, and apply the security patch as part of your next maintenance window.

sudo dnf update python3-mako

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET.*\/{2}\.\.\/.*\.(txt|conf|key|secret|env|sql|yaml|json|py|sh)

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Block HTTP requests containing double-slash path traversal sequences (//../) before they reach the template engine. Implement a WAF rule: SecRule ARGS|REQUEST_URI "@rx //{2}.*\.\.\/" "id:1000,phase:2,deny,status:403,msg:'Path traversal attempt detected'"

How to check if you are affected

  1. Step 1: Check installed Mako version by running: python3 -c "import mako; print(mako.__version__)"
  2. Step 2: Verify if your application uses Mako's TemplateLookup class by searching source code for: grep -r "TemplateLookup" /path/to/app
  3. Step 3: Search application logs for suspicious URI patterns like //../../../ or double-slash paths passed to template handlers: grep -E '//\.\./|//../' /var/log/app.log
  4. Step 4: Confirm the patch is installed by running: python3 -c "import mako; print('Patched' if mako.__version__ >= '1.3.11' else 'Vulnerable')"

Indicators of compromise

  • URI pattern: //../../../etc/passwd
  • URI pattern: //../../../root/.ssh/id_rsa
  • Request header containing: GET //../../../secret.txt HTTP/1.1

FAQ

What is CVE-2026-41205?

CVE-2026-41205 is a path traversal vulnerability in Mako's template lookup mechanism that allows attackers to bypass directory restrictions and read any file accessible to the Python process by crafting URIs with leading double slashes (e.g., //../../../secret.txt).

Is CVE-2026-41205 being actively exploited?

No, CVE-2026-41205 is not currently listed in the CISA Known Exploited Vulnerabilities catalog, and no public exploits have been disclosed. However, the vulnerability is trivial to exploit if user input reaches TemplateLookup.get_template().

What versions of Python are affected by CVE-2026-41205?

The vulnerability affects Mako template library versions prior to 1.3.11. Mako is available as a Python package regardless of Python version (3.6+), so any system running Mako before version 1.3.11 is at risk.

How do I check if my server is vulnerable to CVE-2026-41205?

Run: python3 -m pip show mako | grep Version. If the version is earlier than 1.3.11, your system is vulnerable. Also verify your application accepts user input in template lookup calls with: grep -r "get_template" /path/to/app

Does Defensia detect CVE-2026-41205?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Mako is installed on a monitored server, CVE-2026-41205 will appear in your dashboard with remediation steps.

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References

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