Screenshot Burp Agent Skill

Screenshot: Burp Repeater request/response PoC

Turn a Burp Repeater exchange into a report-ready request + response image. This is the Burp-native

counterpart to Skill(screenshot) (curl/terminal cards): when you drive a target through Burp, capture

the proof FROM Burp. Prereqs are the same as Skill(hunt-burp) (Burp running + the MCP Server BApp, SSE

on 127.0.0.1:9876; verify with bash /root/vm.sh 'python3 ~/burp-mcp-cli.py list').

One command (use this)

scripts/capture.sh burp <eng> <slug> <host> <port> <https:true|false> <method> <path> [bodyfile] [tabname]
# POST with a body file (forged/complex bodies -> write to a file, avoids shell quoting):
scripts/capture.sh burp thm_x flag1 10.1.1.1 5000 true  POST /login /tmp/login_body.txt "ECorp login"
# simple GET:
scripts/capture.sh burp thm_x flag3 10.1.1.1 3000 false GET  /challenge/solve

It: (1) create_repeater_tab via the MCP with the raw request, (2) activates Burp on the seat display,

focuses the request editor, sends with Ctrl+Space (Burp's Repeater Send hotkey), (3) import-grabs

the window and pulls targets/<eng>/poc/NN-<slug>.png, printing the ! ref. Drop that ref into

walkthrough.md so the image actually renders in Obsidian (an un-referenced PNG in poc/ is invisible

in the notes - only reachable by opening the folder).

Crypto-forged / signed requests: give the exploit script a --curl-style mode that writes the exact

body to a file (e.g. /tmp/login_body.txt), then pass it as bodyfile. The Repeater tab then holds the

real forged request, so the PoC is Burp-native and reproducible.

Gotchas baked into capture.sh burp (the burp mode) (why hand-rolling this failed the first time)

• Grab as the SEAT user, not root. Burp may be root-owned but it DRAWS on the desktop user's X

session (the desktop login on :0). who -> the line with a (:N) display gives the user + display; use their

~/.Xauthority. A root-over-SSH grab has no X display.

• Send = Ctrl+Space (KEYBOARD only); mouse is dead. Java Swing IGNORES synthetic xdotool MOUSE clicks

(button/tab/pixel clicks are silent no-ops), but KEYBOARD events land once the window is activated

(windowactivate --sync): Ctrl+Shift+R (focus Repeater), Ctrl+= (next sub-tab), Ctrl+Space (Send).

Drive everything by keyboard; anything with no hotkey (e.g. the BApp MCP tab) needs a human mouse action.

• Window offset: getwindowgeometry -> the client area sits at screen (0, ~35); the import -window

grab starts at the client top, so screen_y = image_y + 35 (only matters if you ever DO need a click on a

WM that accepts synthetic clicks; this one does not).

• Write the grab to a WORLD-WRITABLE path (/tmp/capture_burp_*.png), never a root-owned -o dir: the

sudo-as-seat-user import can't write into /tmp/poc if root created it (silent EACCES = "no PNG").

• The "SSE wedge" was a MISDIAGNOSIS (corrected 2026-07-24). The only MCP call that ever hung is

send_http1_request, and that is the extension's target-approval gate (a non-approved target raises a

GUI approval prompt a headless seat cannot answer -> 15s timeout), NOT a per-session wedge. create_repeater_tab,

get_active_editor_contents, url_encode, set_proxy_intercept_state all run fine across many back-to-back

per-call sessions. capture.sh burp never calls send_http1_request (it Sends in the GUI via Ctrl+Space,

human-equivalent, which bypasses the approval gate), so it is unaffected. If create_repeater_tab itself

fails, the server is down/unreachable -> check scripts/burp/burp-transport.sh (see [[burp-mcp]]).

Selecting the finding's tab (SOLVED 2026-07-24, Burp 2026.3.x, verified end-to-end)

create_repeater_tab appends the tab RIGHTMOST but does NOT focus it, so a naive grab caught whatever tab was

last active (the old stale-tab PoCs). capture.sh burp now SELECTS the intended tab deterministically and

VERIFIES it before Send/grab, so a wrong-tab PoC is impossible. The sequence (all baked into the burp mode):

• Unlock + wake the seat FIRST. A Kali screen LOCK (seat0) routes synthetic input to the locker, so

getmouselocation over Burp reports window:0 and NO key/click lands -- burpshot then silently caught the

wrong tab. loginctl unlock-session <seat0-sid> (root) dismisses the lock; xset dpms force on + xset s off

(seat user) wake the display. Without this a locked/idle VM fails the precheck. (shot.py already did this;

capture.sh burp now does too.)

• Interactivity precheck = mouse getmouselocation over Burp returns the Burp WID (not window:0). This is

the RELIABLE check; wmctrl -lG is NOT -- it reports "no managed windows" on this no-WM seat even when input

lands, a false negative.

• SELECT by keyboard + oracle. Ctrl+= (go_to_next_tab, it WRAPS) steps sub-tabs; after each step read

get_active_editor_contents and stop when it shows the created request's METHOD PATH line (cap 16, fail loud

if never confirmed). The old "Ctrl+= does not move the tab" finding was from the LOCKED-seat era when no input

landed at all -- once unlocked, Ctrl+= selects the tab AND focuses its editor, which the oracle reads. (Marker

= the request line; a distinctive path keeps it unambiguous -- identical request-lines across tabs match the

first found.)

• Send + grab. Ctrl+Space sends the now-confirmed tab; import -window $WID grabs it. The run prints

GRAB_OK ... (verified tab: <marker>); a GRAB_FAIL tells you why (locked seat the unlock did not clear, or

MCP down -> burp-transport.sh).

CAPTURE was never the problem: import -window works headless; flameshot FAILS on this seat ("Unable to

capture screen" -- no DBus/portal in the minimal X), so for a tighter crop use `import -window $WID -crop

WxH+X+Y +repage or maim/scrot -a` (pure X11), never flameshot here.

Manual fallback (what the script automates)

# 1) stage the request as a Repeater tab (root, via MCP)
bash /root/vm.sh 'python3 ~/burp-mcp-cli.py call create_repeater_tab "{\"content\":\"GET /x HTTP/1.1\r\nHost: T:80\r\nConnection: close\r\n\r\n\",\"targetHostname\":\"T\",\"targetPort\":80,\"usesHttps\":false}"'
# 2) send + grab as the seat user (detect the desktop user + display from `who`)
bash /root/vm.sh 'U=$(who | awk "/\(:[0-9]/{print \$1;exit}"); D=$(who|grep -oE "\(:[0-9]+"|head -1|tr -d "(")
  sudo -u "$U" env DISPLAY="$D" XAUTHORITY=/home/$U/.Xauthority bash -c "
  WID=\$(xdotool search --name \"Burp Suite Professional\" | head -1)
  xdotool windowactivate --sync \$WID; xdotool mousemove 500 400 click 1; sleep .4
  xdotool key ctrl+space; sleep 4; import -window \$WID /tmp/burp.png"'
# 3) pull it
bash /root/vm.sh 'base64 -w0 /tmp/burp.png' | base64 -d > targets/<eng>/poc/NN-slug.png

Redaction / boundary

Same as Skill(screenshot): images live only under targets/<eng>/ (gitignored); run Skill(evidence)

before a client report (Burp responses can carry cookies/PII). Never embed in wiki/.

Output

Report: the poc/NN-slug.png saved + the ! ref added to walkthrough.md; note if the MCP wedged

(and whether you restarted it or fell back to the proxy).