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

How to Fix CVE-2026-20420: Path Traversal in MediaTek chipset

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

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityNot verified - see advisory
Actively exploited?Not currently listed in CISA KEV
AffectedMT2735, MT2737, MT6813, MT6815, MT6833, MT6835, and others
Fixed inSee vendor advisory
Type (CWE)CWE-125: Out-of-bounds Read

What is CVE-2026-20420?

CVE-2026-20420 is a path traversal flaw in MediaTek chipset. The product fails to canonicalize or restrict file paths supplied by a remote caller, so .. sequences or absolute paths reach restricted parts of the filesystem. Vendor description: In Modem, there is a possible system crash due to incorrect error handling. This could lead to remote denial of service, if a UE has connected to a rogue base station controlled by the attacker, with no additional execution privileges needed.

Why this CVE matters

Path traversal flaws look low-impact on paper but routinely chain into full compromise. An attacker who can read arbitrary files often pulls configuration secrets, session databases, or private keys, and many traversal bugs also allow writes that drop a webshell into the document root.

For deployments of MediaTek chipset 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 MediaTek chipset'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-2026-20420

  1. Read the vendor advisory in full: https://corp.mediatek.com/product-security-bulletin/February-2026
  2. Upgrade MediaTek chipset 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).

Generic patch procedure


# Confirm the patched build against the vendor advisory: https://corp.mediatek.com/product-security-bulletin/February-2026
# 1. Identify the running version of MediaTek, Inc. MediaTek chipset.
which mediatek-chipset && mediatek-chipset --version || true
dpkg -l | grep -i mediatek-chipset || rpm -qa | grep -i mediatek-chipset || true

# 2. Pull the patched build from the vendor's distribution channel.
#    Target: the build named in the vendor advisory

# 3. Apply per the vendor's documented upgrade procedure (installer / package
#    manager / firmware utility).

# 4. Restart the affected service so the patched binary loads.
sudo systemctl restart <service-name>

# 5. Confirm the running version matches the advisory's fixed build.
mediatek-chipset --version


# Windows equivalent: pull current updates and confirm product version.
Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -Confirm:$false
Get-WindowsUpdate -AcceptAll -Install -AutoReboot
Get-CimInstance Win32_Product | Where-Object { $_.Name -match 'MediaTek chipset' } |
  Select-Object Name, Version

Verify the fix landed


# Confirm the patched build against the vendor advisory: https://corp.mediatek.com/product-security-bulletin/February-2026
# 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-2026-20420 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

Block requests containing ../, ..%2f, or absolute path prefixes at a reverse proxy. Restrict access to the affected endpoint to trusted networks. Apply the patched build as the real fix.

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-2026-20420 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-2026-20420?

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 MediaTek chipset 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.*