⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Medium · CVSS 6.9

How to Fix CVE-2026-2147: Information Disclosure in AC21

Other vulnerabilities in the same area that are worth patching alongside this one:

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 6.9 - Medium
Actively exploited?Not currently listed in CISA KEV
Affected16.03.08.16
Fixed inSee vendor advisory
Type (CWE)CWE-200: Information Disclosure

What is CVE-2026-2147?

CVE-2026-2147 is an information disclosure flaw in AC21. The product returns sensitive data to a caller who should not have access, including credentials, session tokens, or configuration. Disclosure often feeds a follow-up attack chain. Vendor description: A weakness has been identified in Tenda AC21 16.03.08.16. This impacts an unknown function of the file /cgi-bin/DownloadLog of the component Web Management Interface.

Why this CVE matters

Information disclosure flaws are dangerous because they make the next attack easier. Sensitive configuration, session material, or credentials leaked from one endpoint frequently power the follow-on attack that actually takes over the system.

For deployments of AC21 that have been exposed to the public internet during the disclosure window, the operating assumption should be that scanning has already happened. Even where exploitation has not been publicly observed, scanning for the vulnerable fingerprint is cheap and routine. Patching closes the door; log review and credential rotation close out the rest of the response.

Am I affected?

You are affected if your installation matches any of these version ranges:

Check your installed version against the list above. If you cannot determine the version, treat the system as affected and follow the upgrade path below.

Open AC21's About dialog or run the vendor-documented version-check command. Compare the result against the affected ranges in the advisory.

How to fix CVE-2026-2147

  1. Read the vendor advisory in full: https://vuldb.com/?id.344849
  2. Upgrade AC21 to the patched build listed in the vendor advisory.
  3. Back up the configuration (and database, where applicable) before upgrading.
  4. Apply the patch in a maintenance window. For HA pairs, upgrade the standby node first, fail over, then upgrade the former primary.
  5. Restart the affected service so the patched binary loads, then verify the new version (see verification section).

npm / Yarn / pnpm


# Confirm the patched build against the vendor advisory: https://vuldb.com/?id.344849
# Update to the patched release <patched-version-from-advisory>.
npm install ac21@<patched-version-from-advisory>
# Alternative pinning:
npm install ac21@latest
npm ls ac21

PyPI (pip / Poetry)


# Confirm the patched build against the vendor advisory: https://vuldb.com/?id.344849
pip install --upgrade "ac21==<patched-version-from-advisory>"
pip show ac21 | grep -i version

# Poetry equivalent:
poetry add ac21@<patched-version-from-advisory>

Docker / container


# Confirm the patched build against the vendor advisory: https://vuldb.com/?id.344849
docker pull <your-registry>/ac21:<patched-version-from-advisory>
docker stop <app> && docker rm <app>
docker run -d --name <app> <your-registry>/ac21:<patched-version-from-advisory>
docker image inspect <your-registry>/ac21:<patched-version-from-advisory> --format '{{.Id}}'

Verify the fix landed


# Confirm the patched build against the vendor advisory: https://vuldb.com/?id.344849
# 1. Confirm the running version equals the advisory's fixed-in build.
#    (Use the platform-specific version probe from the commands above.)

# 2. Re-scan with your vulnerability scanner (Nessus, Qualys, Tenable, OpenVAS).
#    The scanner should no longer flag CVE-2026-2147 on the patched target.

# 3. Inspect recent service and kernel logs for crash-loops or rollback events.
journalctl --since "10 minutes ago" | tail -200
dmesg --since "10 minutes ago" | tail -100

If you cannot patch immediately

Restrict access to the management interface to trusted internal IP addresses only. Block public access at the firewall and require VPN for any remote administration. Apply the patch as soon as a maintenance window allows.

How to verify the fix worked

If your installation was internet-reachable during the disclosure window, treat log review as part of the remediation rather than an optional follow-up. Look for unusually long URI paths containing traversal sequences, unexpectedly large responses from the affected endpoint, and outbound requests from the application to internal addresses or cloud-metadata endpoints. Treat any sensitive file the bug could disclose as exposed.

Frequently asked questions

Is CVE-2026-2147 being exploited in the wild?

Public exploitation has not been confirmed by CISA at the time of writing. Treat the patch as time-sensitive anyway; reports often lag actual abuse.

Will a WAF or IDS rule fully mitigate CVE-2026-2147?

No. Network-layer filters can reduce noise and slow opportunistic scanners, but they will not stop a determined attacker. The vendor patch is the only durable fix.

How long should I plan for the upgrade?

Typical vendor-documented upgrade windows for AC21 run from a few minutes to under an hour depending on cluster size. Test in a staging environment first and follow the vendor's documented HA upgrade order.

References

*This guide was assembled from the official vendor advisory, the NVD record, and the CISA KEV catalog entry on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*