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rpuga's avatar
rpuga
Icon for Nimbostratus rankNimbostratus
Jun 27, 2018

ASM: Failed to convert character

Hello everyone,

 

I have an application protected by ASM using charset UTF-8. What happens is that sometimes I get some false-positives because the user browser is not using the charset informed in the meta tag. For instance, in some tests using Chrome and having as input some strings like “weißbier” or “über” I have no problems, but when I use Internet Explorer 11, ASM blocks the request with this error.

 

There is an article from Microsoft about this saying that IE does not always take the specified charset in the page but it might be overridden by OS settings:

 

https://support.microsoft.com/en-us/help/928847/internet-explorer-uses-the-wrong-character-set-when-it-renders-an-html

 

So my question is, how do you deal with this? I wouldn't like to disable this check in the Security Policy, any possible alternatives?

 

ASM Advanced WAF
character
charset
convert
ie
internet explorer
security

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  • Renato's avatar
    Renato
    Icon for Altostratus rankAltostratus
    Jun 27, 2018

    If you know which one is the problematic client and the policy element affected, you are able to allow traffic when it happens using iRule.

    Something like this:

    when ASM_REQUEST_VIOLATION
{
    set asmdata [ASM::violation_data]
    if {([lindex $asmdata 0] contains "VIOLATION_CHAR_CONV")}
    {
        if { [string tolower [HTTP::header User-Agent]] contains "msie" }
        {
            ASM::unblock
        }
    }
}