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We are encountering issues in our production environment with 100% CPU utilization and thread dump shows our "Black List" implementation stuck on following.
[11/14/13 10:12:42:745 CST] 0000000d ThreadMonitor W WSVR0605W: Thread "Thread-002" (0000003b) has been active for 604063 milliseconds and may be hung. There is/are 1 thread(s) in total in the server that may be hung.
at java.lang.Character.isLetterOrDigit(Character.java:3516)
at java.util.regex.Pattern$Bound.check(Pattern.java:4820)
at java.util.regex.Pattern$Bound.match(Pattern.java:4832)
at java.util.regex.Pattern$Curly.match0(Pattern.java:3782)
at java.util.regex.Pattern$Curly.match(Pattern.java:3744)
at java.util.regex.Pattern$BmpCharProperty.match(Pattern.java:3366)
at java.util.regex.Pattern$Curly.match0(Pattern.java:3782)
at java.util.regex.Pattern$Curly.match(Pattern.java:3744)
at java.util.regex.Matcher.match(Matcher.java:1127)
at java.util.regex.Matcher.matches(Matcher.java:502)
The problem is this does not happen always which mean it is data dependent and we have following list of Regular Expressions in our Black List implementation.
I would appreciate if someone can tell which regular expression out of the following can potentially cause the 100% CPU (I would guess due to back tracking).
# zero/null bytes
.*\x00.*
# javascript
.*\bjavascript\b.* &&! ^[\w.,;/*+= -]*\b(:?application/x-javascript|text/javascript)\b[\w.,;/*+= -]*$
# vbscript
.*\bvbscript\b.*
# <script or </script>
.*<\s*/?\s*script\b.*|.*\bscript\s*>.*
# <img or </img>
.*<\s*/?\s*img\b.*|.*\bimg\s*>.*
# <div or </div>
.*<\s*/?\s*div\b.*|.*\bdiv\s*>.*
# <html or </html>
.*<\s*/?\s*html\b.*|.*\bhtml\s*>.*
# <body or </body>
.*<\s*/?\s*body\b.*|.*\bbody\s*>.*
# <link or </link>
.*<\s*/?\s*link\b.*|.*\blink\s*>.* &&! ^<\?xml .*$
# <meta or </meta>
.*<\s*/?\s*meta\b.*|.*\bmeta\s*>.*
# <base or </base>
.*<\s*/?\s*base\b.*|.*\bbase\s*>.*
# <span or </span>
.*<\s*/?\s*span\b.*|.*\bspan\s*>.*
# <input or </input>
.*<\s*/?\s*input\b.*|.*\binput\s*>.*
# <style or </style>
.*<\s*/?\s*style\b.*|.*\bstyle\s*>.*
# <table or </table>
.*<\s*/?\s*table\b.*|.*\btable\s*>.*
# <embed or </embed>
.*<\s*/?\s*embed\b.*|.*\bembed\s*>.*
# <frame or </frame>
.*<\s*/?\s*frame\b.*|.*\bframe\s*>.*
# <iframe or </iframe>
.*<\s*/?\s*iframe\b.*|.*\biframe\s*>.*
# <object or </object>
.*<\s*/?\s*object\b.*|.*\bobject\s*>.*
# < onload= >
.*<.+\bonload\s*=.+>.*
# < onerror= >
.*<.+\bonerror\s*=.+>.*
# < onmouseover= >
.*<.+\bonmouseover\s*=.+>.*
# < src= >
.*<.+\bsrc\s*=.+>.*
# < href= >
.*<.+\bhref\s*=.+>.*
# < style= >
.*<.+\bstyle\s*=.+>.*
# < content= >
.*<.+\bcontent\s*=.+>.*
# document.
.*\bdocument\s*\..+
# element.
.*\belement\s*\..+
# url(
.*\burl\s*\(.+
# eval(
.*\beval\s*\(.+
# alert(
.*\balert\s*\(.+
# /* */
.*/\*.*\*/.*
# HTTP response splitting
.*\bHTTP/\d+\.\d+.+
# Path traversal
#.*\.\.[/\\].*
.*\.\.[/\\]\.\.[/\\].*
# SQL injection (probably not very useful)
# from HttpServletBase.java
.*select\s+\S*\s*from\s+\S+(?:\s+where\s+.+)?.*
.*insert\s+\S*\s*into\s+\S+(?:\s+values\s+.+)?.*
.*update\s+\S*\s*set\s+\S+(?:\s+where\s+.+)?.*
.*delete\s+\S*\s*from\s+\S+(?:\s+where\s+.+)?.*
753
asked Apr 18 '26 04:04
As I say in the comments, proper testing of the data is the only way to really know which regex is problematic. But I think there is something I can pinpoint and you can look into. Basically, be careful about the dot operator.
Look at:
.*<.+\bonload\s*=.+>.*
I guess you want to find any HTML tag that contains "onload". The thing is, if you have data with a lot of tags, and none contain "onload", it will do like this:
<< in the string.This will therefore be repeated for every tag in the string, so step 2 can be expensive if your string is long. You can optimize by preventing it to go past the end of the tag by replacing .+ with [^>]+ (that is, anything but a >).
So the following regex should perform better:
.*<[^>]+\bonload\s*=.+>.*
Also, following the general principle that "the fastest code is the code that doesn't run", you can look if the string contains the string "onload" with a simple string search before using a regular expression.
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