June 14, 2021

PHP Floating-Point bug Found and then Fixed

phpA bug has been found in the popular web site scripting language PHP which theoretically could be used in a DoS attack against a web site. The bug is related to the way PHP 5.2 and 5.3 convert largest double-precision floating-point numbers from strings. The number in question is 2.2250738585072011e-308 and if a script wants to convert this from a string the CPU goes into an infinite loop. This could theoretically be used to mount a denial of service attack on a web site and send the CPU into overdrive.

The problem is known to only affect x86 32-bit PHP processes, regardless of whether the system hosting PHP is 32-bit or 64-bit. This is because 32-bit PHP processes use the x87 FPU for doing the conversion where as 64-bit processes use SSE.

The PHP team saw this as a critical bug and have released versions 5.3.5 and 5.2.17 to tackle the problem. It is strongly recommended that you upgrade to the new versions.

For more details see on the bug see the PHP bug report here and news of the new releases here. You can test whether your system is affected by running this script from the command line.

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