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Fencer Vulns
medium 5.0

CVE-2026-55244 json

ASTEVAL: Sandbox Escape via BaseException Subclasses

published 2026-08-20 2 mo ago modified 2026-09-30 39 d ago also GHSA-89v8-rhwq-hf77 , PYSEC-2026-3807 , EUVD-2026-78058

cvss
5.0
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 7%
public exploits
0
none known

Summary

ASTEVAL is an evaluator of Python expressions and statements. Prior to 1.0.9, FROM_PY in asteval/astutils.py exposes BaseException, SystemExit, KeyboardInterrupt, and GeneratorExit to expressions evaluated by asteval.Interpreter.eval(), while run() and eval() in asteval/asteval.py catch Exception rather than these non-Exception BaseException subclasses. When an attacker-controlled expression raises one of these classes, on_raise() passes the class to raise_exception(), and the resulting exception bypasses the interpreter's safety handlers and propagates into the calling application. A consuming service that evaluates untrusted expressions can therefore be terminated or have signal and cleanup handling disrupted, causing denial of service. The separately documented read-only open() capability is not part of this vulnerability. This issue is fixed in version 1.0.9.

Patch / fix

  • pypi asteval 1.0.9
  • python-asteval openSUSE Tumbleweed 1.0.9-1.1

opensuse advisories openSUSE-SU-2026:11420-1

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
53 d ago

Exploit prediction

0.18% chance of exploitation in the next 30 days, higher than 7% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/lmfit/asteval/security/advisories/GHSA-89v8-rhwq-hf77 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.0 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
OSV 3.1 5.0 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
GitHub 3.1 5.0 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi asteval
<1.0.9
1.0.9

Affected products

  • lmfit asteval

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.