RFC 1194
Finger User Information Protocol
RFC 1194 🎀 is called The Finger User Information Protocol ✨. It came from the Network Working Group 🌸 and was written by D. Zimmerman at the Center for Discrete Mathematics and Theoretical Computer Science 🧠. It's dated November 1990 📅 and it's an IAB standards track protocol 💅, so it's an actual official standard and not just vibes. It obsoletes RFC 742 🦋. The header doesn't list anything it updates 🫶.
Status of this Memo 💅
This memo defines a protocol for swapping user information around ✨. It's an IAB standards track protocol for the Internet community, and it's asking for discussion and suggestions to make it better 💖. For the standardization state and status of this protocol, go check the current edition of the "IAB Official Protocol Standards" 📚. Distribution of this memo is unlimited 🌈.
Abstract 🦋
This memo describes the Finger User Information Protocol 💜. It's a simple protocol that gives you an interface to a remote user information program ✨.
Based on RFC 742, which is the write-up of the original Finger protocol, this memo tries to clarify what the two ends of a Finger connection expect from each other 🫶. It also tries not to break the many existing implementations or add unnecessary restrictions to the original protocol definition 🙈.
Table of Contents 📑
1. Introduction ........................................... 2
1.1. Intent ............................................... 2
1.2. History .............................................. 3
1.3. Requirements ......................................... 3
2. Use of the protocol .................................... 3
2.1. Flow of events ....................................... 3
2.2. Data format .......................................... 4
2.3. Query specifications ................................. 4
2.4. RUIP {Q2} behavior ................................... 4
2.5. Expected RUIP response ............................... 5
2.5.1. {C} query .......................................... 5
2.5.2. {U}{C} query ....................................... 6
2.5.3. {U} ambiguity ...................................... 6
2.5.4. /W query token ..................................... 6
2.5.5. Vending machines ................................... 7
3. Security ............................................... 7
3.1. Implementation security .............................. 7
3.2. RUIP security ........................................ 7
3.2.1. {Q2} refusal ....................................... 7
3.2.2. {C} refusal ........................................ 8
3.2.3. Atomic discharge ................................... 8
3.2.4. User information files ............................. 8
3.2.5. Execution of user programs ......................... 9
3.2.6. {U} ambiguity ...................................... 9
3.2.7. Audit trails ....................................... 9
3.3. Client security ...................................... 9
4. Examples ............................................... 10
4.1. Example with a null command line ({C}) ............... 10
4.2. Example with name specified ({U}{C}) ................. 10
4.3. Example with ambiguous name specified ({U}{C}) ....... 11
4.4. Example of query type {Q2} ({U}{H}{H}{C}) ............ 11
5. Acknowledgments ........................................ 12
6. Security Considerations ................................ 12
7. Author's Address ....................................... 121. Introduction 🎀
1.1. Intent ✨
So this memo is all about the Finger User Information Protocol 💖. It's a simple protocol that gives you an interface to a remote user information program (RUIP) ✨.
Based on RFC 742, the original Finger protocol write-up, this memo tries to clarify what the two ends of a Finger connection expect from each other 🫶. It also tries not to break the many current implementations or add unnecessary restrictions to the original protocol definition 💅.
The most prevalent implementations of Finger today seem to be mostly derived from the BSD UNIX work at the University of California, Berkeley 🏫. Thus, this memo is based around the BSD version's behavior 🌸.
Here's the tea though 🫢. The BSD version gives you few options to tailor the Finger RUIP for a particular site's security policy, or to protect the user from dangerous data 😬. Furthermore, there are MANY potential security holes that implementors and administrators need to be aware of 🚨. This is extra spicy because the whole point of this protocol is to return information about a system's users, which is a sensitive issue at best 💀. Therefore, this memo makes a number of important security comments and recommendations 🔒.
1.2. History 📜
The FINGER program at SAIL, written by Les Earnest, was the inspiration for the NAME program on ITS 🧚. Earl Killian at MIT and Brian Harvey at SAIL were jointly responsible for implementing the original protocol 🙌.
Ken Harrenstien is the author of RFC 742, "Name/Finger", which this memo began life as 🦋.
1.3. Requirements 📏
Okay so, in this doc, the words that tell you how important each requirement is get capitalized 🔠. Here they are:
- "MUST": This word or the adjective "REQUIRED" means that the item is an absolute requirement of the specification.
- "SHOULD": This word or the adjective "RECOMMENDED" means that there may exist valid reasons in particular circumstances to ignore this item, but the full implications should be understood and the case carefully weighed before choosing a different course.
- "MAY": This word or the adjective "OPTIONAL" means that this item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because it enhances the product, for example; another vendor may omit the same item.
So an implementation is not compliant if it fails to satisfy one or more of the MUST requirements 🚫. An implementation that satisfies all the MUST and all the SHOULD requirements is "unconditionally compliant" 👑. One that satisfies all the MUST requirements but not all the SHOULD requirements is "conditionally compliant" 🥹.
2. Use of the protocol 🧚
2.1. Flow of events 🌊
Finger runs on top of the Transmission Control Protocol and uses TCP port 79 decimal (that's 117 in octal) 🔌. Here's how it goes. A TCP connection gets opened to a remote host on the Finger port 🚪. Then an RUIP shows up on the far end of that connection to handle the request 🧚. The RUIP gets sent a one line query based on the Finger query specification 📝. It processes the query, sends back an answer, and then closes the connection normally 👋.
2.2. Data format 🔤
Any data transferred MUST be in ASCII format, with no parity, and with lines ending in CRLF 💻. That means other character formats like EBCDIC, etc. are out 🙅. It also means that any characters between ASCII 128 and ASCII 255 should truly be international data, not USASCII with the parity bit set 🌍.
2.3. Query specifications 🔍
An RUIP MUST accept the entire Finger query specification 🫶.
The Finger query specification is defined:
{Q1} ::= [{U}] [/W] {C}
{Q2} ::= [{U}]{H} [/W] {C}
{U} ::= username
{H} ::= @hostname | @hostname{H}
{C} ::= <CRLF>{H}, being recursive, means that there is no arbitrary limit on the number of @hostname tokens in the query 🌀. In examples of the {Q2} request specification, the number of @hostname tokens is limited to two, simply for brevity ✂️.
Be aware that {Q1} and {Q2} do not refer to a user typing finger user@host from an operating system prompt 👀. They refer to the line that an RUIP actually receives. So if a user types finger user@host<CRLF>, the RUIP on the remote host receives user<CRLF>, which corresponds to {Q1} 💅.
Just like everything in the IP protocol suite, "be liberal in what you accept" 🌷.
2.4. RUIP {Q2} behavior 🔁
A query of {Q2} is a request to forward a query to another RUIP 🪞. An RUIP MUST either provide or actively refuse this forwarding service (see section 3.2.1) 🙅♀️. If an RUIP provides this service, it MUST conform to the following behavior:
So picture this, given that:
Host <H1> opens a Finger connection <F1-2> to an RUIP on host
<H2>.
<H1> gives the <H2> RUIP a query <Q1-2> of type {Q2}
(e.g., FOO@HOST1@HOST2).From that, it should be derived that:
Host <H3> is the right-most host in <Q1-2> (i.e., HOST2)
Query <Q2-3> is the remainder of <Q1-2> after removing the
right-most "@hostname" token in the query (i.e., FOO@HOST1)And so:
The <H2> RUIP then must itself open a Finger connection <F2-3>
to <H3>, using <Q2-3>.
The <H2> RUIP must return any information received from <F2-3>
to <H1> via <F1-2>.
The <H2> RUIP must close <F1-2> in normal circumstances only
when the <H3> RUIP closes <F2-3>.2.5. Expected RUIP response 🎤
For the most part, the output of an RUIP doesn't follow a strict specification, since it's meant to be read by people instead of programs 🧑💻. It should mainly strive to be informative ✨.
Output of ANY query is subject to the discussion in the security section 🔐.
2.5.1. {C} query 🌟
A query of {C} is a request for a list of all online users 👀. An RUIP MUST either answer or actively refuse (see section 3.2.2). If it answers, then it MUST provide at least the user's full name 📛. The system administrator SHOULD be allowed to include other useful information (per section 3.2.3), such as:
- terminal location
- office location
- office phone number
- job name
- idle time (number of minutes since last typed input, or since last job activity)
2.5.2. {U}{C} query 🕵️
A query of {U}{C} is a request for in-depth status of a specified user {U}. If you really want to refuse this service, you probably don't want to be running Finger in the first place 😅.
An answer MUST include at least the full name of the user. If the user is logged in, at least the same amount of information returned by {C} for that user MUST also be returned by {U}{C} 🫶.
Since this is a query for information on a specific user, the system administrator SHOULD be allowed to choose to return additional useful information (per section 3.2.3), such as:
- office location
- office phone number
- home phone number
- status of login (not logged in, logout time, etc)
- user information file
A user information file is a feature where a user may leave a short message that gets included in the response to Finger requests 📄. (This is sometimes called a "plan" file 🗓️.) It's easy to build by, for example, having the program look for a specially named text file in the user's home directory or some common area 🏠. The exact method is up to the implementor 🛠️. The system administrator SHOULD be allowed to specifically turn this feature on and off 🔀. See section 3.2.4 for caveats ⚠️.
There MAY be a way for the user to run a program in response to a Finger query 🤯. If this feature exists, the system administrator SHOULD be allowed to specifically turn it on and off 🔛. See section 3.2.5 for caveats 🚨.
2.5.3. {U} ambiguity 🤔
Allowable "names" in the command line MUST include "user names" or "login names" as defined by the system 🏷️. If a name is ambiguous, the system administrator SHOULD be allowed to choose whether or not all possible derivations should be returned in some fashion (per section 3.2.6) 🧩.
2.5.4. /W query token ✨
okay bestie, the /W token in {Q1} or {Q2} queries SHOULD at best get read by the last RUIP as a "give me more verbosity" signal in the user info output 🔊. At worst it just gets ignored, and honestly that's fine too 💅
2.5.5. Vending machines 🍓
vending machines SHOULD respond to a {C} request with a list of all items currently available for purchase and possible consumption 🍫. for a {U}{C} request, they SHOULD respond with a detailed count or list of the particular product or product slot 🥤. vending machines should NEVER NEVER EVER eat requests. or money. 💀😭
3. Security 🔐
3.1. Implementation security
Sound implementation of Finger is of the utmost importance 🔥. Implementations should be tested against various forms of attack 🧪. Especially, an RUIP SHOULD protect itself against malformed inputs 🛡️. Vendors that ship Finger with the operating system or network software should subject their implementations to penetration testing 🕵️♀️.
Finger is one of the avenues for direct penetration, as the Morris worm pointed out quite vividly 😬. Like Telnet, FTP and SMTP, Finger is one of the protocols sitting at the security perimeter of a host 🚪. Accordingly, the soundness of the implementation is paramount 👑. The implementation should receive just as much security scrutiny during design, implementation, and testing as Telnet, FTP, or SMTP 🔍.
3.2. RUIP security
Warning!! 🚨 Finger discloses information about users; moreover, such information may be considered sensitive 🙈. Security administrators should make explicit decisions about whether to run Finger and what information should be provided in responses. One existing implementation provides the time the user last logged in, the time he last read mail, whether unread mail was waiting for him, and who the most recent unread mail was from! 👀 This makes it possible to track conversations in progress and see where someone's attention was focused. Sites that are information-security conscious should not run Finger without an explicit understanding of how much information it is giving away.
3.2.1. {Q2} refusal 🚫
For individual site security concerns, the system administrator SHOULD be given an option to individually turn on or off RUIP processing of {Q2} 🎛️. If RUIP processing of {Q2} is turned off, the RUIP MUST return a service refusal message of some sort. "Finger forwarding service denied" is adequate 🙅♀️. The purpose of this is to allow individual hosts to choose to not forward Finger requests, but if they do choose to, to do so consistently 🤝.
Overall, there are few cases which would warrant processing of {Q2} at all, and they are far outweighed by the number of cases for refusing to process {Q2}. In particular, be aware that if a machine is part of the security perimeter (that is, it is a gateway from the outside world to some set of interior machines), then turning {Q2} on provides a path through that security perimeter 🌉. Therefore, it is RECOMMENDED that the default of the {Q2} processing option be to refuse processing. It certainly should not be enabled in gateway machines without careful consideration of the security implications 🫣.
3.2.2. {C} refusal 🙊
For individual site security concerns, the system administrator SHOULD be given an option to individually turn on or off RUIP acceptance of {C} 🎚️. If RUIP processing of {C} is turned off, the RUIP MUST return a service refusal message of some sort. "Finger online user list denied" is adequate. The purpose of this is to allow individual hosts to choose to not list the users currently online 🙃.
3.2.3. Atomic discharge ⚛️
All implementations of Finger SHOULD allow individual system administrators to tailor what atoms of information are returned to a query 🧩. For example:
- Administrator A should be allowed to specifically choose to return office location, office phone number, home phone number, and logged in/logout time.
- Administrator B should be allowed to specifically choose to return only office location, and office phone number.
- Administrator C should be allowed to specifically choose to return the minimum amount of required information, which is the person's full name.
3.2.4. User information files 📄
Allowing an RUIP to return information out of a user-modifiable file should be seen as equivalent to allowing any information about your system to be freely distributed 📢. That is, it is potentially the same as turning on all specifiable options. This information security breach can be done in a number of ways, some cleverly, others straightforwardly 🥷. This should disturb the sleep of system administrators who wish to control the returned information 😴.
3.2.5. Execution of user programs 🏃♀️
Allowing an RUIP to run a user program in response to a Finger query is potentially dangerous ⚠️.
BE CAREFUL!! -- the RUIP MUST NOT allow system security to be compromised by that program.
Implementing this feature may be more trouble than it is worth, since there are always bugs in operating systems, which could be exploited via this type of mechanism 🐛.
3.2.6. {U} ambiguity 🕵️
Be aware that a malicious user's clever and/or persistent use of this feature can result in a list of most of the usernames on a system 😬. Refusal of {U} ambiguity should be considered in the same vein as refusal of {C} requests (see section 3.2.2) 🔁.
3.2.7. Audit trails 📒
Implementations SHOULD allow system administrators to log Finger queries 📝.
3.3. Client security 💻
It is expected that there will normally be some client program that the user runs to query the initial RUIP 🖥️. By default, this program SHOULD filter any unprintable data, leaving only the USASCII characters and CRLF. This is to protect against people playing with VT100 escape codes and changing other peoples' X window names, or committing other dastardly deeds 😈. Two separate user options SHOULD be considered to modify this behavior, so that users may choose to view international data or control characters:
- one to allow characters less than ASCII 32
- another to allow characters greater than ASCII 126
For environments that live and breathe international data, the system administrator SHOULD be given a mechanism to enable these options by default for all users on a particular system 🌍. This can be done via a global environment variable or similar mechanism.
4. Examples 📚
4.1. Example with a null command line ({C})
here's what it looks like when the command line is empty 🫙:
Site: elbereth.rutgers.edu
Command line: <CRLF>
Login Name TTY Idle When Office
rinehart Mark J. Rinehart p0 1:11 Mon 12:15 019 Hill x3166
greenfie Stephen J. Greenfiel p1 Mon 15:46 542 Hill x3074
rapatel Rocky - Rakesh Patel p3 4d Thu 00:58 028 Hill x2287
pleasant Mel Pleasant p4 3d Thu 21:32 019 Hill 908-932-
dphillip Dave Phillips p5 021: Sun 18:24 265 Hill x3792
dmk David Katinsky p6 2d Thu 14:11 028 Hill x2492
cherniss Cary Cherniss p7 5 Mon 15:42 127 Psychol x2008
harnaga Doug Harnaga p8 2:01 Mon 10:15 055 Hill x2351
brisco Thomas P. Brisco pe 2:09 Mon 13:37 h055 x2351
laidlaw Angus Laidlaw q0 1:55 Mon 11:26 E313C 648-5592
cje Chris Jarocha-Ernst q1 8 Mon 13:43 259 Hill x24134.2. Example with name specified ({U}{C})
Site: dimacs.rutgers.edu
Command line: pirmann<CRLF>
Login name: pirmann In real life: David Pirmann
Office: 016 Hill, x2443 Home phone: 989-8482
Directory: /dimacs/u1/pirmann Shell: /bin/tcsh
Last login Sat Jun 23 10:47 on ttyp0 from romulus.rutgers.
No unread mail
Project:
Plan:
Work Schedule, Summer 1990
Rutgers LCSR Operations, 908-932-2443
Monday 5pm - 12am
Tuesday 5pm - 12am
Wednesday 9am - 5pm
Thursday 9am - 5pm
Saturday 9am - 5pm
larf larf hoo hoo4.3. Example with ambiguous name specified ({U}{C})
Site: elbereth.rutgers.edu
Command line: ron<CRLF>
Login name: spinner In real life: Ron Spinner
Office: Ops Cubby, x2443 Home phone: 463-7358
Directory: /u1/spinner Shell: /bin/tcsh
Last login Mon May 7 16:38 on ttyq7
Plan:
ught i
ca n
m a
' ... t
I . . i
! m
! ! e
p !pool
l
e
H
Login name: surak In real life: Ron Surak
Office: 000 OMB Dou, x9256
Directory: /u2/surak Shell: /bin/tcsh
Last login Fri Jul 27 09:55 on ttyq3
No Plan.
Login name: etter In real life: Ron Etter
Directory: /u2/etter Shell: /bin/tcsh
Never logged in.
No Plan.4.4. Example of query type {Q2} ({U}{H}{H}{C})
Site: dimacs.rutgers.edu
Command line: hedrick@math.rutgers.edu@pilot.njin.net<CRLF>
[pilot.njin.net]
[math.rutgers.edu]
Login name: hedrick In real life: Charles Hedrick
Office: 484 Hill, x3088
Directory: /math/u2/hedrick Shell: /bin/tcsh
Last login Sun Jun 24 00:08 on ttyp1 from monster-gw.rutge
No unread mail
No Plan.5. Acknowledgments 🫶
Thanks to everyone in the Internet Engineering Task Force for their comments 💕. Special thanks to Steve Crocker for his security recommendations and prose 🌟.
6. Security Considerations 🔒
Security issues are discussed in Section 3 💜.
7. Author's Address 🖊️
David Paul Zimmerman
Center for Discrete Mathematics and
Theoretical Computer Science
Rutgers University
P.O. Box 1179
Piscataway, NJ 08855-1179
Phone: (908)932-4592
EMail: dpz@dimacs.rutgers.edu📦 where this page comes from
- ietf: rfc1194 1990-11
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms