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How badly should I try to prevent a user from XSSing themselves?

2

Let's say a user can store some data in a web app. I'm now only talking about that sort of data the user can THEMSELVES view, not that is intended to be viewed by other users of the webapp. (Or if other users may view this data then it is handled to them in a more secure way.)

How horrible would it be to allow some XSS vulnerability in this data?

Of course, a purist's answer would clearly be: "No vulnerabilities are allowed". But honestly - why?

Everything that is allowed is the user XSSing THEMSELVES. What's the harm here? Other users are protected. And I can't see a reason why would someone mount an attack against themselves (except if it is a harmless one, in which case - again - no harm is done).

My gut feelings are that the above reasoning will raise some eyebrows... OK, then what am I failing to see?

xss attacks

share|improve this question

asked 7 hours ago

gaazkamgaazkam

1,3162819

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How can you limit the scope of an XSS vuln to just some data? This is asking to open the door to everything getting compromised. Don't be lazy with it
  
  – Crumblez
  7 hours ago
  

  
  
  
  

add a comment | 

2

Let's say a user can store some data in a web app. I'm now only talking about that sort of data the user can THEMSELVES view, not that is intended to be viewed by other users of the webapp. (Or if other users may view this data then it is handled to them in a more secure way.)

How horrible would it be to allow some XSS vulnerability in this data?

Of course, a purist's answer would clearly be: "No vulnerabilities are allowed". But honestly - why?

Everything that is allowed is the user XSSing THEMSELVES. What's the harm here? Other users are protected. And I can't see a reason why would someone mount an attack against themselves (except if it is a harmless one, in which case - again - no harm is done).

My gut feelings are that the above reasoning will raise some eyebrows... OK, then what am I failing to see?

xss attacks

share|improve this question

asked 7 hours ago

gaazkamgaazkam

1,3162819

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How can you limit the scope of an XSS vuln to just some data? This is asking to open the door to everything getting compromised. Don't be lazy with it
  
  – Crumblez
  7 hours ago
  

  
  
  
  

add a comment | 

Let's say a user can store some data in a web app. I'm now only talking about that sort of data the user can THEMSELVES view, not that is intended to be viewed by other users of the webapp. (Or if other users may view this data then it is handled to them in a more secure way.)

How horrible would it be to allow some XSS vulnerability in this data?

Of course, a purist's answer would clearly be: "No vulnerabilities are allowed". But honestly - why?

Everything that is allowed is the user XSSing THEMSELVES. What's the harm here? Other users are protected. And I can't see a reason why would someone mount an attack against themselves (except if it is a harmless one, in which case - again - no harm is done).

My gut feelings are that the above reasoning will raise some eyebrows... OK, then what am I failing to see?

xss attacks

share|improve this question

asked 7 hours ago

gaazkamgaazkam

1,3162819

share|improve this question

asked 7 hours ago

gaazkamgaazkam

1,3162819

share|improve this question

asked 7 hours ago

gaazkamgaazkam

1,3162819

asked 7 hours ago

gaazkamgaazkam

1,3162819

asked 7 hours ago

gaazkamgaazkam

1,3162819

2 Answers
2

active

oldest

votes

4

This is actually a real concept, "Self XSS" which is sufficiently common that if you open https://facebook.com and then open the developer tools, they warn you about it

Obviously Facebook is a specific type of target and whether this issue matters to you or not, would depend on the exact nature of your site, but you may not be able to discount the idea of one user using social engineering techniques to get another user to attack themselves.

share|improve this answer

answered 7 hours ago

Rоry McCuneRоry McCune

52.7k13113187

add a comment | 

0

Although you are right in that it might not matter so much from an attack point of view. From a usability point of view, the user might come across some 'unexpected behavior'. A while ago I used to have to work with software that had an obvious SQL injection problem (contractors couldn't/wouldn't fix it). This meant that unexpecting users would enter in something seemingly harmless such as their name "O'Brien", which would trigger an SQL injection and for computer illiterate people it was unexpected behavior. It is probably less likely with XSS, however consider the following if a user uses <> instead of () the data might seem to disappear. A proof of concept is below:

<html>

    <head><title>HI</title></head>

    <body>

        <h1>WEBSITE</h1>

        Hey my name is <travis>.

    </body>

</html>

Note that when this website is rendered, the word 'travis', is not rendered.

share|improve this answer

answered 6 hours ago

meowcatmeowcat

1644

add a comment | 

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4

This is actually a real concept, "Self XSS" which is sufficiently common that if you open https://facebook.com and then open the developer tools, they warn you about it

Obviously Facebook is a specific type of target and whether this issue matters to you or not, would depend on the exact nature of your site, but you may not be able to discount the idea of one user using social engineering techniques to get another user to attack themselves.

share|improve this answer

answered 7 hours ago

Rоry McCuneRоry McCune

52.7k13113187

add a comment | 

4

This is actually a real concept, "Self XSS" which is sufficiently common that if you open https://facebook.com and then open the developer tools, they warn you about it

Obviously Facebook is a specific type of target and whether this issue matters to you or not, would depend on the exact nature of your site, but you may not be able to discount the idea of one user using social engineering techniques to get another user to attack themselves.

share|improve this answer

answered 7 hours ago

Rоry McCuneRоry McCune

52.7k13113187

add a comment | 

This is actually a real concept, "Self XSS" which is sufficiently common that if you open https://facebook.com and then open the developer tools, they warn you about it

Obviously Facebook is a specific type of target and whether this issue matters to you or not, would depend on the exact nature of your site, but you may not be able to discount the idea of one user using social engineering techniques to get another user to attack themselves.

share|improve this answer

answered 7 hours ago

Rоry McCuneRоry McCune

52.7k13113187

share|improve this answer

answered 7 hours ago

Rоry McCuneRоry McCune

52.7k13113187

answered 7 hours ago

Rоry McCuneRоry McCune

52.7k13113187

answered 7 hours ago

Rоry McCuneRоry McCune

52.7k13113187

0

Although you are right in that it might not matter so much from an attack point of view. From a usability point of view, the user might come across some 'unexpected behavior'. A while ago I used to have to work with software that had an obvious SQL injection problem (contractors couldn't/wouldn't fix it). This meant that unexpecting users would enter in something seemingly harmless such as their name "O'Brien", which would trigger an SQL injection and for computer illiterate people it was unexpected behavior. It is probably less likely with XSS, however consider the following if a user uses <> instead of () the data might seem to disappear. A proof of concept is below:

<html>

    <head><title>HI</title></head>

    <body>

        <h1>WEBSITE</h1>

        Hey my name is <travis>.

    </body>

</html>

Note that when this website is rendered, the word 'travis', is not rendered.

share|improve this answer

answered 6 hours ago

meowcatmeowcat

1644

add a comment | 

0

Although you are right in that it might not matter so much from an attack point of view. From a usability point of view, the user might come across some 'unexpected behavior'. A while ago I used to have to work with software that had an obvious SQL injection problem (contractors couldn't/wouldn't fix it). This meant that unexpecting users would enter in something seemingly harmless such as their name "O'Brien", which would trigger an SQL injection and for computer illiterate people it was unexpected behavior. It is probably less likely with XSS, however consider the following if a user uses <> instead of () the data might seem to disappear. A proof of concept is below:

<html>

    <head><title>HI</title></head>

    <body>

        <h1>WEBSITE</h1>

        Hey my name is <travis>.

    </body>

</html>

Note that when this website is rendered, the word 'travis', is not rendered.

share|improve this answer

answered 6 hours ago

meowcatmeowcat

1644

add a comment | 

Although you are right in that it might not matter so much from an attack point of view. From a usability point of view, the user might come across some 'unexpected behavior'. A while ago I used to have to work with software that had an obvious SQL injection problem (contractors couldn't/wouldn't fix it). This meant that unexpecting users would enter in something seemingly harmless such as their name "O'Brien", which would trigger an SQL injection and for computer illiterate people it was unexpected behavior. It is probably less likely with XSS, however consider the following if a user uses <> instead of () the data might seem to disappear. A proof of concept is below:

<html>

    <head><title>HI</title></head>

    <body>

        <h1>WEBSITE</h1>

        Hey my name is <travis>.

    </body>

</html>

Note that when this website is rendered, the word 'travis', is not rendered.

share|improve this answer

answered 6 hours ago

meowcatmeowcat

1644

<html>

    <head><title>HI</title></head>

    <body>

        <h1>WEBSITE</h1>

        Hey my name is <travis>.

    </body>

</html>

share|improve this answer

answered 6 hours ago

meowcatmeowcat

1644

answered 6 hours ago

meowcatmeowcat

1644

answered 6 hours ago

meowcatmeowcat

1644