Kestra OSS: code execution flaw under attack

What is affected

Kestra OSS is mostly run by companies, schools and public bodies, not on home computers. You are unlikely to have it yourself, but organisations that hold your data may. Breaches that start with flaws like this one are how personal data ends up leaked.

Kestra OSS contains an OS command injection vulnerability that could allow an unauthenticated remote attacker to create and execute arbitrary workflows without credentials.

What an attacker can do

This is a code execution flaw. It lets an attacker run their own commands or programs on the affected system. In practice that usually means taking it over: installing malware, stealing data or using it to reach other devices on the same network.

How it is reached

Over the internet or network

Access the attacker needs

No account needed

Does the victim have to do something?

No, works without the victim doing anything

What to do

1. At home: nothing to install. Keep your own devices updated and use a different password for every service, so that a breach at one organisation does not open your other accounts.
2. If you administer Kestra OSS at work: apply the vendor's fix or mitigation now and review logs for signs of compromise, because the flaw was being exploited before it was listed.
3. If the product is past its support date and no fix exists, take it off the internet or retire it.

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Vendor advisories and fixes

• github.comgithub.com/kestra-io/kestra/security/advisories/GHSA-5vc5-wxxq-3fjx

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on September 2, 2026, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by September 5, 2026, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 2.1% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 81% of all scored vulnerabilities.

Its CVSS severity score is 10.0 out of 10 (critical), as recorded in the US National Vulnerability Database.

Technical description

Kestra is an open-source, event-driven orchestration platform. Prior to 1.0.45 and 1.3.21, AuthenticationFilter in Kestra OSS uses request.getPath().endsWith("/configs") to whitelist the public configuration endpoint from Basic Auth. Because the check is a suffix match rather than an exact path match, any API path whose last segment is configs bypasses authentication entirely. An unauthenticated remote attacker can exploit this to create and execute arbitrary workflows without credentials. Because Kestra ships with script execution plugins (plugin-script-shell, plugin-script-python, etc.) enabled by default, this directly results in unauthenticated Remote Code Execution as root inside the Kestra worker container. This vulnerability is fixed in 1.0.45 and 1.3.21.