The Zyxel WX3100-T0 (Dual-Band Wireless AX1800 Gigabit Access Point/Extender) is a service-provider product, so its firmware is deliberately absent from the consumer Download Library — that page serves only the user’s guide, quick start guide, datasheet and CE declarations. The service-provider product page is no better, and Zyxel’s own security advisories tell you to contact a sales representative for the patch file.

The files are nonetheless sitting on Zyxel’s public CDN, unauthenticated and unlisted. This note records the URL scheme so the next person (or the next me) does not have to rediscover it.

Latest firmware

V5.50(ABVL.5.1)C0 — 18.7 MB, published 14 July 2026:

https://download.zyxel.com/WX3100-T0/firmware/WX3100-T0_5.50(ABVL.5.1)C0.zip

This is the ceiling, not merely the newest I happened to find: it matches the patch version named in Zyxel’s advisory of 21 July 2026 (CVE-2026-6952, post-authentication command injection in the syslog LogServer field), which lists WX3100-T0 as affected at “5.50(ABVL.5)C0 and earlier”.

The URL scheme

https://download.zyxel.com/WX3100-T0/firmware/WX3100-T0_{VERSION}.zip

The trap is that the router and the extender use different schemes on different hosts. The sibling DX3300-T0 router lives at:

https://spdl.zyxel.com/DX3300-T0/firmware(public_version)/DX3300-T0_Firmware_5.50(ABVY.7.2)C0.zip

Three differences, all of which must be undone for the extender: host spdl → download, folder firmware(public_version) → firmware, and the _Firmware_ infix dropped so the filename is just MODEL_VERSION.zip. Guessing the extender URL from the router’s fails on all three counts, which is presumably why it is not common knowledge.

Model codes are worth noting too: ABVL is the WX3100-T0, ABVY is the DX3301/DX3300/EX3301/EX3300-T0 family. Mixing them up produces plausible-looking URLs that do not exist.

Every build actually published

Version Size Published
5.50(ABVL.0)C0 15.5 MB 10 Apr 2026
5.50(ABVL.1.1)C0 15.8 MB 10 Apr 2026
5.50(ABVL.4)C0 17.6 MB 10 Apr 2026
5.50(ABVL.4.1)C0 17.6 MB 10 Apr 2026
5.50(ABVL.4.2)C0 17.6 MB 10 Apr 2026
5.50(ABVL.4.3)C0 17.6 MB 10 Apr 2026
5.50(ABVL.4.4)C0 17.6 MB 10 Apr 2026
5.50(ABVL.4.6)C0 17.7 MB 10 Apr 2026
5.50(ABVL.4.7)C0 17.7 MB 10 Apr 2026
5.50(ABVL.4.8)C0 18.3 MB 10 Apr 2026
5.50(ABVL.4.9)C0 18.0 MB 10 Apr 2026
5.50(ABVL.5)C0 18.9 MB 14 Jul 2026
5.50(ABVL.5.1)C0 18.7 MB 14 Jul 2026

Confirmed absent: 4.5, 4.10, 4.11+, 5.2+, 6.x, any 5.70 build, and the Y0 suffix variants. Two of those gaps matter:

  • The advisory of 28 April 2026 (CVE-2026-0711) names 4.10 as its patch, but that build was never published here. 5.1 supersedes it, so it is moot.
  • The user’s guide covers “V5.17_5.70”, but no 5.70 firmware exists for this model. Do not go looking for it.

Probing for future releases

The CDN returns HTTP 200 for missing files, serving a 114-byte HTML redirect stub to download_landing.shtml. Status codes are therefore useless for existence checks — test the Content-Type instead. A real file is application/x-zip-compressed; a miss is text/html.

probe() {
  url="https://download.zyxel.com/WX3100-T0/firmware/WX3100-T0_5.50(ABVL.$1)C0.zip"
  h=$(curl -sI -m 10 --globoff "$url")
  ct=$(echo "$h" | tr -d '\r' | awk 'tolower($1)=="content-type:"{print $2}')
  cl=$(echo "$h" | tr -d '\r' | awk 'tolower($1)=="content-length:"{print $2+0}')
  [ "$ct" = "application/x-zip-compressed" ] &&
    awk -v v="$1" -v c="$cl" 'BEGIN{printf "%-8s %.1f MB\n", v, c/1048576}'
}

for n in 5.1 5.2 5.3 6 6.1; do probe "$n"; done

Sanity-check any hit with a 4-byte range request before trusting it — a genuine archive starts PK\003\004:

curl -s --globoff -r 0-3 \
  "https://download.zyxel.com/WX3100-T0/firmware/WX3100-T0_5.50(ABVL.5.1)C0.zip" | od -c

Before you flash

Read the current version first, from the extender’s web UI (default http://192.168.1.2) under Maintenance → Firmware Upgrade.

Check the suffix letter. Every file in the public repository is C0 (generic). Older Y0 builds exist, such as 5.50(ABVL.2.1)Y0, and those are ISP-customised images. A unit running a non-C0 build is on an ISP’s own track, is typically updated only via TR-069, and will often refuse a generic image outright. If one device on a network has stubbornly stayed behind while its siblings updated, this is the first thing to check — it will save you a flash attempt the bootloader was never going to accept.

Mind the gap below 4. Note the size cliff in the table: 15.8 MB at 1.1 against 17.6 MB at 4, with no 2.x or 3.x build published at all. That discontinuity suggests a platform change across the boundary. Upgrading from 0 or 1.1 may well work directly, but if 5.1 is rejected, stage it 1.1 → 4.7 → 5.1. Devices already on the 4.x line go straight to 5.1 with no structural jump.

Risk context. WAN management is disabled by default on these units and CVE-2026-6952 requires authenticated administrator access, so if a device is on a stable older build and not exposed, the urgency is mild. Worth weighing against the fact that several users reported instability on the 4.4 build.

A note on OpenWrt

There is no third-party route here. The OpenWrt support thread documents the hardware — ECONET EN7516GT SoC, 256 MB RAM, 128 MB W25N01G flash, MediaTek MT7975DN and MT7905DEN radios, UART pins populated by default — but the SoC is unsupported and a moderator’s verdict is that support is “not going to happen”. No community mirrors or reuploads exist either, which is moot now the official host is known.

These are Zyxel’s own unauthenticated CDN URLs, not mirrors. They are unlisted rather than secret, which also means Zyxel is free to move or withdraw them without notice — if a link here dies, re-run the probe above rather than assuming the build is gone.