Summary
Open WebUI: Instance-wide stall via automation recurrence rules that force multi-second parsing
In every affected release, automation recurrence parsing anchors minutely and hourly rules at a fixed date of 2000-01-01 and then walks forward one interval at a time to find the next run. A single FREQ=MINUTELY rule therefore enumerates roughly a quarter-century of occurrences, synchronously, on the event loop that also serves the scheduler, HTTP and WebSocket traffic. Nothing bounds the walk, and nothing moves it off the loop.
Preconditions
Any user who can create an automation. USER_PERMISSIONS_FEATURES_AUTOMATIONS defaults to false, so on a default deployment only an admin can reach the create path; it becomes reachable by ordinary users on any deployment that has granted the automations feature, which is the normal way to make the feature usable. UVICORN_WORKERS defaults to 1, so there is no second worker to absorb the stall. The rule needs no unusual syntax: FREQ=MINUTELY with no DTSTART, or with a DTSTART set well in the past, is enough.
Root cause
Affected component: backend/open_webui/utils/automations.py, _parse_rule, reached from the automation create, update and toggle handlers in backend/open_webui/routers/automations.py and from the scheduler's claim path in backend/open_webui/models/automations.py. Affected setup: every build from 0.9.0 onward, since that is when the automations feature shipped.
The fixed anchor existed to make sub-daily intervals snap to clock boundaries, so that "every 5 minutes" lands on :00, :05, :10 rather than drifting from whenever the automation happened to be created. Snapping only needs a reference point of the right phase, but the implementation used a literal far-past date as that reference and left the recurrence library to walk forward from it. The distance between the anchor and the present is therefore attacker-influenced work that grows with real time, and it was never treated as a cost that needed a bound or a thread.
Proof of concept
Measured cost of a single next-run computation against the shipped 0.10.2 parser:
| rule | cost |
|---|---|
RRULE:FREQ=MINUTELY |
18,880 ms |
RRULE:FREQ=MINUTELY;BYSECOND=0,1,2,3,4,5,6,7,8,9 |
64,236 ms |
DTSTART:20000101T000000 + RRULE:FREQ=MINUTELY |
26,237 ms |
RRULE:FREQ=HOURLY |
339 ms |
Measured at function level deliberately. Persisting such an automation has the scheduler repeat the walk on every poll and wedge the instance indefinitely, which is the actual impact but makes a live end-to-end run destructive to the test instance.
Credits
Reported by @Classic298.
Impact
Availability, against every other user of the instance. One evaluation of RRULE:FREQ=MINUTELY takes 18.9 s of blocking CPU; adding a ten-value BYSECOND list multiplies the walk and takes 64.2 s. FREQ=HOURLY costs 0.34 s and is not materially exploitable on its own. The cost does not stop at creation: once the automation is stored, the scheduler recomputes the next run for every claimed row on each poll, so the same walk repeats on a default 10 s interval and the instance stays wedged rather than recovering. Instances that have not enabled the automations feature for non-admin users are exposed only to an admin doing this.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-70489 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.11.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Fixed in 0.11.0. Sub-daily rules are now anchored to the current clock instead of the year-2000 date, so the walk starts at the next occurrence rather than a quarter-century behind it. A caller-supplied DTSTART is honoured only when the number of occurrences it implies stays under a fixed bound, and is otherwise replaced by the clock-aligned anchor. The same rules that cost 18.9 s and 64.2 s now cost under a millisecond. Upgrading fully resolves the issue, no configuration change is required.
Frequently Asked Questions
- What is CVE-2026-70489? CVE-2026-70489 is a medium-severity uncontrolled resource consumption vulnerability in open-webui (pip), affecting versions >= 0.9.0, < 0.11.0. It is fixed in 0.11.0. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-70489? CVE-2026-70489 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of open-webui are affected by CVE-2026-70489? open-webui (pip) versions >= 0.9.0, < 0.11.0 is affected.
- Is there a fix for CVE-2026-70489? Yes. CVE-2026-70489 is fixed in 0.11.0. Upgrade to this version or later.
- Is CVE-2026-70489 exploitable, and should I be worried? Whether CVE-2026-70489 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-70489 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-70489? Upgrade
open-webuito 0.11.0 or later.