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 .
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
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/heymrun/heym/security/advisories/GHSA-87x2-9jwx-7gh4 (vendor-advisory)
- www.vulncheck.com/advisories/heym-before-0.0.91-remote-code-execution-via-expre… (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.