T09 · Insecure Skill Coding Practices
- Location
SKILL.md:397- Finding
Unsafe Non-Atomic Firewall Rule Modification Can Cause Service Lockout
- Content
View full analysis
Vulnerability Details
File Location:
SKILL.md, lines 397-402
Vulnerability Type: Unsafe firewall configuration and unvalidated remote input
Risk Level: HighVulnerable Code
bash CF_IPS=$(curl -s https://www.cloudflare.com/ips-v4) # ... for ip in $CF_IPS; do iptables -A INPUT -p tcp -s "$ip" --dport 443 -j ACCEPT done iptables -A INPUT -p tcp --dport 443 -j DROPTechnical Analysis
The documented procedure retrieves a remote IP list and uses its contents directly to construct privileged firewall rules. It does not:
- Make
curlfail on HTTP or transport errors. - Verify that the response is nonempty and complete.
- Validate each value as an expected IPv4 address or CIDR.
- Apply the rules atomically through a dedicated chain or
iptables-restore. - preserve existing administrative or service access explicitly.
- Provide a rollback mechanism.
- Prevent duplicate rules when run repeatedly.
The final DROP rule is unconditional. If retrieval fails or returns an incomplete response, the loop may install no ACCEPT rules—or only a partial set—before blocking all remaining inbound HTTPS traffic. Because
iptablesmodification ordinarily requires elevated privileges, following this recipe can make system-wide networking changes.Although the IP list is retrieved remotely, it is consumed as firewall configuration data rather than executed as code. The primary issue is therefore insecure configuration handling rather than remote payload execution.
Attack Path
- An operator or AI agent executes the documented recipe with sufficient privileges to modify firewall rules.
- The Cloudflare IP-list request fails, is truncated, or produces unexpected content.
- Because
curl -sdoes not enforce successful retrieval and the response is not validated, execution continues. - No valid ACCEPT rules, or only an incomplete set of rules, are appended.
- The unconditional port ...[truncated 870 chars]
- Make
- Remediation
View remediation
Remediation Suggestions
- Retrieve the list with strict failure handling, such as
curl --fail --show-error --silent, and abort if retrieval fails. - Store the response in a controlled temporary file and verify that it is nonempty.
- Validate every entry against a strict IPv4 CIDR parser before constructing any firewall rule.
- Reject the entire update if any entry is malformed or if the number of valid ranges is unexpectedly low.
- Build rules in a new dedicated chain and switch traffic to that chain only after all validation and rule creation succeed.
- Prefer an atomic mechanism such as
iptables-restorerather than incrementally appending rules. - Preserve explicit management access and established connections before applying restrictive rules.
- Add an automatic timed rollback that is cancelled only after connectivity is verified.
- Check for existing rules or replace a managed chain instead of appending duplicate rules.
- Require explicit operator confirmation before applying host-wide firewall changes.
- Document tested recovery commands and advise operators to retain console or out-of-band access during deployment.
- Retrieve the list with strict failure handling, such as