--- name: wireshark-e30f4f774585 description: >- Captures and analyzes network traffic with Wireshark and tshark. Use when a user asks to sniff packets, debug a protocol, extract files from PCAPs, inspect TLS handshakes, troubleshoot network latency, or triage a CTF PCAP challenge. license: Apache-2.0 compatibility: 'Wireshark 4.4 / 4.6 (tshark, dumpcap, editcap), Linux/macOS/Windows' metadata: author: terminal-skills version: 1.1.0 category: devops tags: "wireshark, tshark, packet-analysis, network-forensics, pcap" repository: https://gitlab.com/wireshark/wireshark --- # Wireshark ## Overview Wireshark is the dominant packet analyzer. It decodes 3000+ protocols and is the reference for anything from "why is this API slow?" to "extract the exfiltrated ZIP from this PCAP." `tshark` is the CLI companion — use it in scripts, over SSH, or when the capture is too large for the GUI. Capture filters (BPF) trim traffic at capture time; display filters refine what you see afterward. The current stable series is 4.6 (4.6.9); distributions still ship 4.4, and every command here works on both. ## Instructions ### Install and Allow Capture Without Root ```bash sudo apt install tshark # Debian/Ubuntu: CLI only; `wireshark` adds the GUI brew install wireshark # macOS: CLI tools; GUI: brew install --cask wireshark-app winget install WiresharkFoundation.Wireshark # Windows; live capture also needs Npcap (npcap.com), # which the silent install skips # Debian/Ubuntu: let members of the `wireshark` group capture, then join it sudo dpkg-reconfigure wireshark-common # answer "Yes" sudo usermod -a -G wireshark "$USER" # log out and in again ``` Reading a capture file (`-r`) needs no privileges at all. Only the small `dumpcap` helper needs capture rights; running `tshark` or Wireshark itself as root is discouraged because all protocol dissectors then run as root. On macOS with the Homebrew formula, `brew install --cask wireshark-chmodbpf` grants the same access after a reboot (the `wireshark-app` cask already includes it, and the two casks conflict). ### Step 1: Capture Traffic ```bash # List interfaces tshark -D # 1. eth0 # 2. any # 3. lo (Loopback) # Capture to a rolling ring buffer (never fill the disk) tshark -i eth0 -b filesize:100000 -b files:10 -w capture.pcapng # filesize in kB; keeps the last 10 × 100MB files, named capture_00001_20260411120117.pcapng ... # Capture only relevant traffic using a BPF capture filter tshark -i eth0 -f "host 10.0.0.5 and port 443" -w target.pcapng # Stop after a packet count or after a number of seconds tshark -i eth0 -c 1000 -w sample.pcapng tshark -i eth0 -a duration:60 -w one-minute.pcapng # On a server over SSH, pipe into local Wireshark ssh deploy@web-01.internal "sudo tcpdump -U -s0 -w - 'not port 22'" | wireshark -k -i - ``` For unattended captures use `dumpcap` with the same `-i`, `-f`, `-b`, `-a` and `-w` options: it only writes packets and does not dissect them, so it uses little memory. ### Step 2: Filter in the GUI or CLI ```bash # Display filters (different syntax from capture filters!) # Capture filter: "tcp port 80" # Display filter: "tcp.port == 80" # Read a PCAP and apply a display filter tshark -r capture.pcapng -Y "http.request.method == POST" tshark -r capture.pcapng -Y "ip.src == 10.0.0.5 and tcp.flags.syn == 1" tshark -r capture.pcapng -Y "dns.qry.name contains \"ledgerline.dev\"" tshark -r capture.pcapng -Y "tls.handshake.type == 1" # Client Hello # Common display filter cheatsheet # http.request.uri contains "login" # tcp.analysis.retransmission # frame.time >= "2026-04-11 12:00:00" # !(arp or icmp or dns) ``` ### Step 3: Extract Useful Fields ```bash # Pull specific fields as CSV for grep/awk pipelines, pandas or ClickHouse tshark -r capture.pcapng -Y "http.request" -T fields \ -e frame.time_epoch -e ip.src -e ip.dst -e tcp.dstport -e http.host -e http.request.uri \ -E header=y -E separator=, -E quote=d # "1100903354.172938000","10.1.1.101","10.1.1.1","80","10.1.1.1","/" # (frame.time prints "Nov 19, 2004 ..." with a comma inside; use frame.time_epoch for CSV) # Top talkers tshark -r capture.pcapng -q -z conv,ip | head -20 tshark -r capture.pcapng -q -z endpoints,ip # HTTP: packet counts by method and status, then every requested host and URI tshark -r capture.pcapng -q -z http,tree tshark -r capture.pcapng -q -z http_req,tree # TLS server names (SNI) — reveals what hosts a client visited tshark -r capture.pcapng -Y "tls.handshake.type == 1" \ -T fields -e tls.handshake.extensions_server_name | sort -u ``` ### Step 4: Extract Files and Credentials (from PCAPs you own) ```bash # Export HTTP objects (images, scripts, downloads) tshark -r capture.pcapng -q --export-objects http,./http-objects/ # -q: do not also print every packet ls http-objects/ # Extract FTP-DATA transfers tshark -r capture.pcapng -q --export-objects ftp-data,./ftp-files/ # Extract SMB file transfers (other types: tftp, imf, dicom — see --export-objects help) tshark -r capture.pcapng -q --export-objects smb,./smb-files/ # Reconstruct a TCP stream (e.g., unencrypted protocol dump) tshark -r capture.pcapng -q -z follow,tcp,ascii,0 # 0 is the stream index — list the indexes of interesting packets with tshark -r capture.pcapng -Y "ftp-data" -T fields -e tcp.stream | sort -un ``` ### Step 5: Decrypt TLS (with keys you legitimately control) ```bash # Client-side: set SSLKEYLOGFILE before launching the browser export SSLKEYLOGFILE="$HOME/tls-keys.log" firefox & # All session keys are appended as the browser negotiates TLS # In Wireshark: Edit → Preferences → Protocols → TLS → "(Pre)-Master-Secret log filename" # Or via CLI (write $HOME, not ~ — the shell does not expand ~ after the colon): tshark -r traffic.pcapng -o "tls.keylog_file:$HOME/tls-keys.log" \ -Y "http.request" -T fields -e http.host -e http.request.uri # Embed the keys in the capture so it decrypts anywhere without the preference editcap --inject-secrets tls,"$HOME/tls-keys.log" traffic.pcapng traffic-with-keys.pcapng ``` A capture with embedded keys exposes the plaintext to anyone who gets the file — share it accordingly. ## Examples ### Example 1: Diagnose a Slow API Call User: "Requests from this box to api.ledgerline.dev take seconds from time to time. Is it the network?" ```bash # Capture the client's traffic to the API host for one minute tshark -i eth0 -f "host api.ledgerline.dev and port 443" -w slow-api.pcapng -a duration:60 # Retransmissions per second, and the packets themselves tshark -r slow-api.pcapng -q -z io,stat,1,"tcp.analysis.retransmission" tshark -r slow-api.pcapng -Y "tcp.analysis.retransmission or tcp.analysis.duplicate_ack" \ -T fields -e frame.time -e ip.src -e ip.dst -e tcp.seq # Round-trip time: average and worst ACK delay per 5-second interval tshark -r slow-api.pcapng -q \ -z io,stat,5,"AVG(tcp.analysis.ack_rtt)tcp.analysis.ack_rtt","MAX(tcp.analysis.ack_rtt)tcp.analysis.ack_rtt" ``` ``` | Col 1: AVG(tcp.analysis.ack_rtt)tcp.analysis.ack_rtt | | 2: MAX(tcp.analysis.ack_rtt)tcp.analysis.ack_rtt | |------------------------------------------------------| | |1 |2 | | | Interval | AVG | MAX | | |--------------------------------| | | 0 <> 5 | 0.173799 | 1.010145 | | | 5 <> 10 | 0.000373 | 0.001779 | | ``` An interval with a one-second maximum next to sub-millisecond ones, plus retransmissions in the same seconds, points at packet loss on the path. Flat RTT with slow responses means the time is spent in the server: `-Y "tcp.analysis.ack_rtt > 0.1" -T fields -e tcp.stream -e ip.src -e tcp.analysis.ack_rtt` shows which side answers late. ### Example 2: CTF — Extract a File from a PCAP Challenge User: "I got challenge.pcap from a CTF. There should be a file hidden in it." ```bash # Quick triage tshark -r challenge.pcap -q -z io,phs # protocol hierarchy tshark -r challenge.pcap -q -z conv,tcp # conversations # Something interesting on FTP tshark -r challenge.pcap -Y "ftp.request.command == \"RETR\"" \ -T fields -e ftp.request.arg # backup.zip # Pull the transferred file tshark -r challenge.pcap -q --export-objects ftp-data,./ftp/ file ./ftp/* # ./ftp/backup.zip: Zip archive data, made by v3.0 UNIX, extract using at least v1.0 ``` The hierarchy shows `ftp` and `ftp-data` frames under `tcp`, the `RETR` filter names the file, and the export writes it under its original name. If the directory stays empty (tshark could not tie the data connection to a `RETR`), carve the data stream by hand (1 is the `tcp.stream` number of the `ftp-data` packets; the `grep` drops the header lines, which would otherwise corrupt the output): `tshark -r challenge.pcap -q -z follow,tcp,raw,1 | grep -E '^[[:space:]]*[0-9a-f]+$' | xxd -r -p > backup.zip`. ## Guidelines - **Capture only what you are authorized to see.** On shared networks, traffic from other users is off-limits unless your ROE says otherwise. - Capture filters are BPF syntax (`tcp port 443`). Display filters are Wireshark's own (`tcp.port == 443`). Mixing them up is the #1 beginner mistake. - Do not capture with `sudo tshark`: besides the security risk, `dumpcap` then drops every privilege except packet capture, so `-w capture.pcapng` in a directory root does not own fails with "could not be opened: Permission denied". Use the `wireshark` group, or as a last resort write to a root-owned directory. - For long captures, always use ring buffers (`-b filesize:N -b files:N`) so you never fill the disk. - `.pcapng` is preferred over `.pcap` — it stores interface metadata, comments, and per-packet annotations. - Big captures belong in `tshark` or editcap; the GUI becomes slow on multi-gigabyte files. Use `editcap -c 100000 big.pcapng part.pcapng` to split. - TLS decryption needs a key log file from the client process; you cannot decrypt arbitrary TLS sessions without one. - Captures contain credentials, cookies and personal data in the clear. Store and share them as sensitive files, and cut them down with a display filter first: `tshark -r capture.pcapng -Y "ip.addr == 10.0.0.5" -w subset.pcapng`. - Companion tools: `dumpcap` (capture only), `tcpdump` (lighter capture), `mergecap` (combine PCAPs), `editcap` (slice), `capinfos` (summary). --- Source attribution: terminal-skills Original project: https://github.com/TerminalSkills/skills/blob/8a9852d489f274538be9bf1c9121aeb403750b1c/skills/wireshark/SKILL.md License: Apache-2.0 License information: https://www.apache.org/licenses/LICENSE-2.0 Original upstream instructions; downloaded from Dave AI. ## Upstream license notice Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for use, reproduction, and distribution as defined by Sections 1 through 9 of this document. "Licensor" shall mean the copyright owner or entity authorized by the copyright owner that is granting the License. "Legal Entity" shall mean the union of the acting entity and all other entities that control, are controlled by, or are under common control with that entity. For the purposes of this definition, "control" means (i) the power, direct or indirect, to cause the direction or management of such entity, whether by contract or otherwise, or (ii) ownership of fifty percent (50%) or more of the outstanding shares, or (iii) beneficial ownership of such entity. "You" (or "Your") shall mean an individual or Legal Entity exercising permissions granted by this License. "Source" form shall mean the preferred form for making modifications, including but not limited to software source code, documentation source, and configuration files. "Object" form shall mean any form resulting from mechanical transformation or translation of a Source form, including but not limited to compiled object code, generated documentation, and conversions to other media types. "Work" shall mean the work of authorship, whether in Source or Object form, made available under the License, as indicated by a copyright notice that is included in or attached to the work (an example is provided in the Appendix below). "Derivative Works" shall mean any work, whether in Source or Object form, that is based on (or derived from) the Work and for which the editorial revisions, annotations, elaborations, or other modifications represent, as a whole, an original work of authorship. For the purposes of this License, Derivative Works shall not include works that remain separable from, or merely link (or bind by name) to the interfaces of, the Work and Derivative Works thereof. "Contribution" shall mean any work of authorship, including the original version of the Work and any modifications or additions to that Work or Derivative Works thereof, that is intentionally submitted to the Licensor for inclusion in the Work by the copyright owner or by an individual or Legal Entity authorized to submit on behalf of the copyright owner. For the purposes of this definition, "submitted" means any form of electronic, verbal, or written communication sent to the Licensor or its representatives, including but not limited to communication on electronic mailing lists, source code control systems, and issue tracking systems that are managed by, or on behalf of, the Licensor for the purpose of discussing and improving the Work, but excluding communication that is conspicuously marked or otherwise designated in writing by the copyright owner as "Not a Contribution." "Contributor" shall mean Licensor and any individual or Legal Entity on behalf of whom a Contribution has been received by the Licensor and subsequently incorporated within the Work. 2. Grant of Copyright License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare Derivative Works of, publicly display, publicly perform, sublicense, and distribute the Work and such Derivative Works in Source or Object form. 3. Grant of Patent License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer the Work, where such license applies only to those patent claims licensable by such Contributor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed. 4. Redistribution. You may reproduce and distribute copies of the Work or Derivative Works thereof in any medium, with or without modifications, and in Source or Object form, provided that You meet the following conditions: (a) You must give any other recipients of the Work or Derivative Works a copy of this License; and (b) You must cause any modified files to carry prominent notices stating that You changed the files; and (c) You must retain, in the Source form of any Derivative Works that You distribute, all copyright, patent, trademark, and attribution notices from the Source form of the Work, excluding those notices that do not pertain to any part of the Derivative Works; and (d) If the Work includes a "NOTICE" text file as part of its distribution, then any Derivative Works that You distribute must include a readable copy of the attribution notices contained within such NOTICE file, excluding any notices that do not pertain to any part of the Derivative Works, in at least one of the following places: within a NOTICE text file distributed as part of the Derivative Works; within the Source form or documentation, if provided along with the Derivative Works; or, within a display generated by the Derivative Works, if and wherever such third-party notices normally appear. The contents of the NOTICE file are for informational purposes only and do not modify the License. You may add Your own attribution notices within Derivative Works that You distribute, alongside or as an addendum to the NOTICE text from the Work, provided that such additional attribution notices cannot be construed as modifying the License. You may add Your own copyright statement to Your modifications and may provide additional or different license terms and conditions for use, reproduction, or distribution of Your modifications, or for any such Derivative Works as a whole, provided Your use, reproduction, and distribution of the Work otherwise complies with the conditions stated in this License. 5. Submission of Contributions. Unless You explicitly state otherwise, any Contribution intentionally submitted for inclusion in the Work by You to the Licensor shall be under the terms and conditions of this License, without any additional terms or conditions. Notwithstanding the above, nothing herein shall supersede or modify the terms of any separate license agreement you may have executed with Licensor regarding such Contributions. 6. Trademarks. This License does not grant permission to use the trade names, trademarks, service marks, or product names of the Licensor, except as required for reasonable and customary use in describing the origin of the Work and reproducing the content of the NOTICE file. 7. Disclaimer of Warranty. Unless required by applicable law or agreed to in writing, Licensor provides the Work (and each Contributor provides its Contributions) on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. You are solely responsible for determining the appropriateness of using or redistributing the Work and assume any risks associated with Your exercise of permissions under this License. 8. Limitation of Liability. In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall any Contributor be liable to You for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising as a result of this License or out of the use or inability to use the Work (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if such Contributor has been advised of the possibility of such damages. 9. Accepting Warranty or Additional Liability. While redistributing the Work or Derivative Works thereof, You may choose to offer, and charge a fee for, acceptance of support, warranty, indemnity, or other liability obligations and/or rights consistent with this License. However, in accepting such obligations, You may act only on Your own behalf and on Your sole responsibility, not on behalf of any other Contributor, and only if You agree to indemnify, defend, and hold each Contributor harmless for any liability incurred by, or claims asserted against, such Contributor by reason of your accepting any such warranty or additional liability. END OF TERMS AND CONDITIONS Copyright 2025 Terminal Skills Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. # Dave AI resource metadata Creator / publisher: terminal-skills Original project: https://github.com/TerminalSkills/skills/blob/8a9852d489f274538be9bf1c9121aeb403750b1c/skills/wireshark/SKILL.md Attribution basis: Source repository record Fields of work: Development & Engineering, Data & Analytics Roles: DevOps / SRE, Data Analyst, Security Engineer Specialties: Testing, DevOps Tools: Wireshark, Tshark Country applicability: Country not specified Classification basis: Source category, role and specialization labels Instruction SHA-256: 0ecccbee655143850060de2156241d58ad2d81ae1d83ef1d5fca7d9d72be1305