CVE-2026-52831: Nuclio: Unsanitized cron trigger event headers/body injected into CronJob shell command leads to persistent RCE

Should you act?

Normal patch cycle

No exploitation signal; fix it in your next routine update if you are affected. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.5%, percentile 44: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 44% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs an account (high (admin)). Exposure depends on who can log in.
• Only applies if your dependency tree includes github.com/nuclio/nuclio (Go) < 0.0.0-20260601075854-3356b86a8bfa, fixed in 0.0.0-20260601075854-3356b86a8bfa. Check your lockfile, including transitive dependencies.

What it is

Nuclio is a "Serverless" framework for Real-Time Events and Data Processing. Prior to version 1.16.4, the Nuclio controller builds a curl invocation string for each cron trigger and stores it as the args of a Kubernetes CronJob container (/bin/sh, -c, ). Two fields in the trigger specification flow into this string without adequate sanitization: event.headers keys and event.body. This issue has been patched in version 1.16.4.

From the GitHub advisory

Summary

Nuclio controller builds a curl invocation string for each cron trigger and stores it as the args of a Kubernetes CronJob container (/bin/sh, -c, ). Two fields in the trigger specification flow into this string without adequate sanitization:

- event.headers keys — interpolated verbatim inside double-quoted --header arguments (lazy.go:2150); any key containing " breaks the quoting context. - event.body — processed with strconv.Quote, which escapes " and \ but not $(), allowing command substitution (lazy.go:2188).

Both paths were dynamically verified on Nuclio 1.15.27 (latest as of 2026-05-17).

- CVSS 3.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H — 9.9 (Critical) - CWE: CWE-78 (Improper Neutralization of Special Elements used in an OS Command) - Affected versions: Nuclio

Weakness type: CWE-78.

Product: github.com/nuclio/nuclio (Go) · Assigned by: GitHub_M · Published: 2026-09-02

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: high (needs special conditions)
• Privileges required: high (admin)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.53% probability of exploitation activity in the next 30 days; percentile 44.

Timeline

• 2026-07-08 — GitHub-reviewed advisory GHSA-v5px-423j-pf7p published (critical)
• 2026-09-02 — CVE record published by GitHub_M
• 2026-09-03 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-v5px-423j-pf7p github.com
2. CVE.org record CVE-2026-52831 cve.org
3. NVD entry CVE-2026-52831 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical Go advisories · Today’s Security Digest