RCE in Heymrun Heym
CVE-2026-100864
heym before 0.0.91 contains a sandbox escape vulnerability in the expression engine's DotList map/filter and fallback resolver that allows authenticated users to execute arbitrary Python code. Attackers can craft workflow expressions using dunder attribute access through item expressions or the fallback resolver to access os.system and execute commands as the backend process.
Vulnerability class: RCE (Remote Code Execution)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.009 (58.8th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 58.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.007 · newest: 0.009 · change: +0.002
Affected products
Weakness classification (CWE)
References
- GitHub Security Advisory (GHSA-87x2-9jwx-7gh4) (vendor-advisory)
- VulnCheck Advisory: heym before 0.0.91 Remote Code Execution via Expression Engine (third-party-advisory)
Frequently asked questions
- What is CVE-2026-100864?
- CVE-2026-100864 is a high-severity vulnerability in Heymrun Heym, classified under Code Injection. CVSS score: 8.8/10. Published 2026-09-27.
- How severe is CVE-2026-100864?
- High severity. CVSS v3 base score is 8.8 out of 10.