CVE-2026-70558: Dinky Unauthenticated Arbitrary File Write via /download/uploadFromRsByLocal Gated Only by Hardcoded Default Token
Dinky's POST /download/uploadFromRsByLocal handler passes the caller-supplied path parameter directly to new File(path) and file.transferTo(dest) with no path validation. The route is marked @SaIgnore and /download/ is excluded from the Sa-Token interceptor, so the only guard is a header equality check against a dinkyToken value whose default (efda1551-7958-4e0f-80a8-dfd107df3e38) is hardcoded in source and shipped to every deployment. Anyone who can reach Dinky's HTTP port (8888 by default) and supplies the hardcoded token can write arbitrary files as the Dinky service account. The default Docker image runs on 8888 with no proxy or authentication and chmod 777 on /opt/dinky, so the application's own classpath, launch scripts, and static assets are writable. Demonstrated impact: overwriting /opt/dinky/config/static/index.html served attacker JavaScript to admin browsers immediately, and writing /opt/dinky/org/dinky/Dinky.class executed attacker code as the Dinky service account at the next JVM start via a classpath-shadow launched by script/bin/auto.sh. Writes are uid 9999 (flink), not root, so /etc, /root, /home, and /usr are refused. Affects Dinky v1.2.5 (the current release) and the development branch, where the code is byte-identical.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Configuration
Remove/replace the hardcoded default token value (efda1551-7958-4e0f-80a8-dfd107df3e38) and ensure requests to POST /download/uploadFromRsByLocal are not protected only by the header equality check; enforce real authentication/authorization for this route.
Dinky (HTTP server on port 8888 by default) Authentication/authorization for POST /download/uploadFromRsByLocal (token check) = Require a non-default token and disable unauthenticated access to the handler - Configuration
Remove the @SaIgnore annotation on the uploadFromRsByLocal handler and stop excluding /download/** from the Sa-Token interceptor so the request path is covered by the interceptor guard.
Dinky route /download/** Sa-Token interceptor exclusion /SaIgnore = Enable Sa-Token interception for /download/** and remove @SaIgnore from uploadFromRsByLocal - Compensating control
Restrict network access to Dinky's HTTP port (8888 by default) so only trusted clients can reach it, preventing attackers from reaching the uploadFromRsByLocal endpoint with the token.
- Compensating control
Harden the container filesystem permissions for the default Docker image: avoid chmod 777 on /opt/dinky so the application’s classpath, launch scripts, and static assets cannot be overwritten via arbitrary file write.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-70558?
The severity of CVE-2026-70558 is classified as critical with a score of 9.8.
How do I fix CVE-2026-70558?
To fix CVE-2026-70558, ensure proper path validation is implemented in the POST /download/uploadFromRsByLocal handler.
What type of vulnerability is CVE-2026-70558?
CVE-2026-70558 is a malicious file upload vulnerability that allows arbitrary file writes.
Who is affected by CVE-2026-70558?
Users of the Dinky software that utilize the affected /download/uploadFromRsByLocal endpoint are at risk.
What can exploit CVE-2026-70558?
An attacker can exploit CVE-2026-70558 by sending a specially crafted request with a malicious file path to the vulnerable endpoint.