Kestra CVE-2026-48129

Exploitation requires two specific conditions: first, a Kestra flow must be configured to pass externally supplied data - webhook payload fields or execution input parameters - directly into the file name (key) of an inputFiles task entry, which is a non-default flow design choice made by a developer; second, the attacker must be able to trigger that flow, either through a publicly accessible webhook URL or via whatever access control governs the Kestra execution API. Flows that use only static, developer-defined file names in inputFiles are not exploitable regardless of other configuration. The CVSS AC:H rating reflects the dependency on this specific flow pattern. What limits exploitation: the attacker gains a write-only primitive (no file read, C:N); impact is scoped to the worker node filesystem (S:U); and the vulnerability cannot be exploited against Kestra instances whose flows do not forward external input into inputFiles file names.

The NVD-assigned CVSS 3.1 score of 6.5 (AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L) captures the key risk profile: network-reachable with no credential requirement, but gated by high attack complexity reflecting the prerequisite that a vulnerable flow configuration must exist. The High integrity impact (arbitrary write to the worker filesystem) is significant, while confidentiality is unaffected (no read primitive) and availability impact is Low. No EPSS score was provided in the input data, so exploitation probability cannot be quantified numerically. The vulnerability is not listed in CISA KEV and no public POC has been identified, both of which reduce immediate urgency relative to the raw CVSS score. Real-world risk is materially higher for Kestra deployments that expose webhook-triggered flows accepting user-controlled data and lower for environments using only internal, parameter-controlled flows with static file names. The AC:H metric accurately reflects that this is not a universal exposure - it requires a specific, non-default flow design pattern to be exploitable. Scope is unchanged (S:U), confining impact to the worker host rather than enabling lateral movement to dependent systems at the platform level.

An attacker locates a Kestra instance with a publicly accessible webhook that triggers a flow passing the webhook payload's filename field directly into inputFiles. The attacker sends a crafted HTTP POST containing a file name such as ../../etc/cron.d/pwned, causing the Kestra worker to write attacker-controlled content to an arbitrary path on the worker filesystem. No public POC has been identified, but the attack technique - ../ traversal in an unsanitized file name - is elementary and well-documented in path traversal literature.