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How the Mentioned CVE Works
The vulnerability is a Denial-of-Service (DoS) condition triggered by improper input sanitization of cron expressions within the admin panel. Specifically, the application’s handling of the `scheduled_at` parameter does not validate or escape user-supplied data before writing it to a critical configuration file (backup.yaml). An authenticated attacker (requiring admin panel access) can submit a malformed value, such as a single quote ('), via the `/admin/tools` endpoint. This malicious payload is then persisted directly into the `backup.yaml` file. When the application’s scheduler or a related component attempts to parse the corrupted cron syntax from the YAML file, it throws a fatal error or enters an invalid state. This breaks the admin panel entirely, rendering it inaccessible. Recovery requires direct server access to manually edit the `backup.yaml` file and remove the faulty expression, as the administrative interface is non-functional.
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Platform: Web Application
Version: Unspecified
Vulnerability: Cron Expression DoS
Severity: Medium
Date: 2024-07-24
Prediction: 2024-11-15
What Undercode Say:
Check for recent modifications to the critical YAML file
find /path/to/app -name "backup.yaml" -exec grep -l "scheduled_at" {} \;
cat /path/to/app/config/backup.yaml | grep scheduled_at
Test cron expression validity (example, not the exploit itself)
crontab -l
python3 -c "from crontab import CronTab; tab = CronTab(tab='/5 ')"
Simulate the malformed request leading to DoS
curl -X POST 'http://127.0.0.1/admin/tools' \
-H 'Cookie: sessionid=...' \
--data 'scheduled_at='"'"''
How Exploit:
1. Authenticate to admin panel.
2. Navigate to `/admin/tools`.
- POST request modifying `scheduled_at` parameter to a single quote (
').
4. Payload corrupts `backup.yaml`.
5. Admin panel crashes on access.
Protection from this CVE
Implement input validation.
Sanitize cron expressions.
Use configuration file integrity checks.
Impact:
Admin panel unavailable.
Requires manual server recovery.
Operational disruption.
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Sources:
Reported By: github.com
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