Canvas LMS Incident: Defacement Analysis & Automated Detection
Hey everyone,
Just seeing the reports coming in about the Canvas breach. The scale here is insane—275 million records allegedly held hostage. While we wait for the official root cause analysis (likely an unauthenticated RCE or a compromised SaaS admin account), the immediate threat for those running self-hosted instances is defacement.
If you manage a Canvas instance, I highly recommend checking your login page integrity immediately. The attackers replaced the login portal with a ransom note. Here is a quick Python script to check if your endpoint is serving the defaced content or the legitimate canvas HTML:
import requests
import sys
def check_canvas_status(url):
try:
response = requests.get(url, timeout=5)
# Basic heuristic: checks for missing standard canvas strings or presence of ransom keywords
if "canvas" not in response.text.lower() and "ransom" in response.text.lower():
print(f"[ALERT] Defacement detected at {url}")
else:
print(f"[OK] No obvious defacement at {url}")
except Exception as e:
print(f"[ERROR] Could not reach {url}: {e}")
if __name__ == "__main__":
if len(sys.argv) ")
else:
check_canvas_status(sys.argv[1])
For those on the blue team side, you should be hunting for web shell activity or unusual process execution on your Canvas web servers. We've seen similar groups drop web shells in /public/ directories.
How are you guys handling the internal communications? Are you taking Canvas offline entirely or just blocking external access while you investigate?
Solid script, OP. We're currently hunting for the initial access vector. Our logs show a spike in POST requests to /login/sso shortly before the defacement occurred. It looks like they might have abused the SAML integration to inject the defacement.
If you're running Splunk, try this KQL to spot similar anomalies:
CanvasLogs
| where UrlPath endswith "/login/sso"
| where ResultCode == 200
| summarize count() by bin(TimeGenerated, 5m), SrcIpAddr
| where count_ > 1000
I manage IT for a district using Canvas. We've switched to 'Maintenance Mode' via the admin console and blocked external access at the firewall level until Instructure gives us an all-clear.
It's a nightmare for finals week, but better safe than sorry. We're also forcing a password rotation for all faculty accounts just in case credential stuffing was the entry vector.
From a pentester's perspective, this screams supply chain or a zero-day in the LTI (Learning Tools Interoperability) plugins. Everyone uses those third-party integrations, and they rarely get the same security scrutiny as the core platform.
I'd recommend checking your installed LTI keys and revoking any that aren't strictly necessary right now.
To supplement the manual checks, I suggest automating content monitoring for the login portal. You can set up a simple watchdog script to alert on specific keywords often found in ransom notes. This provides faster feedback than manual verification.
import requests
resp = requests.get("https://your-canvas-instance/login")
if "bitcoin" in resp.text.lower() or "ransom" in resp.text.lower():
print("Defacement Detected")
Good call on the watchdog, Kenji. While monitoring HTML output is smart, don't ignore the backend. If they defaced the page, they likely uploaded a web shell for persistence. I recommend running a quick hash check against known-good backups of the Canvas directory to spot modified binaries.
For those on Linux, use this to find recently modified application files:
find /var/canvas -type f \( -name "*.php" -o -name "*.rb" \) -mtime -1 -ls
This helps catch the persistence mechanism even if you revert the HTML.
Building on Frank's point, checking mtime on the Rails public directory is a quick triage step to find the defacement payload and any backdrops dropped alongside it. You can run this to identify files modified in the last 24 hours:
find /var/www/canvas/public -type f -mtime -1 -ls
Immediately compare those hashes against your repo or backups to verify integrity.
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