IIS/ASP.NET/Umbraco exception on on w3wp.exe and pcre.dll

Question

I have a Windows Server 2025 VPS managed using Plesk for Windows. On it, I host multiple Umbraco websites. Since recently, an issue occurs where some sites' application pools appear to crash, taking that specific whole site offline until they are recycled. I can consistently reproduce it by attempting to sign in to the Umbraco backoffice on a site. In (Chromium) browsers, this yields ERR_HTTP2_PROTOCOL_ERROR. The website/Umbraco logs don't show any peculiarity, while the logs in the Windows Event viewer display following error:

Faulting application name: w3wp.exe, version: 10.0.26100.1882, time stamp: 0xc6bd45bd
Faulting module name: pcre.dll, version: 0.0.0.0, time stamp: 0x63b62f6d
Exception code: 0xc00000fd
Fault offset: 0x0000000000013ecf
Faulting process id: 0x1F24
Faulting application start time: 0x1DBEAD3ACB044B9
Faulting application path: c:\windows\system32\inetsrv\w3wp.exe
Faulting module path: C:\WINDOWS\System32\inetsrv\pcre.dll
Report Id: 05530de0-f951-4855-b3e0-b1ece5a4a8fd
Faulting package full name: 
Faulting package-relative application ID:

The faulting module appears to be an IIS DLL, which makes sense, as multiple sites display this behaviour, although nothing has changed on the system recently to warrant this. I can't find any other info about errors occurring in pcre.dll online, except for this unresolved thread, where a user appears to run into this issue when attempting to authenticate on a non-Umbraco app. Running locally, the sites also work fine. If anyone has any insight, it'd be much appreciated.

Unfortunately, a file in C:\WINDOWS\System32\inetsrv can be made by any vendor (as they can be copied to that folder), not only Microsoft, especially when it is of the version 0.0.0.0 which doesn't even follow a good versioning style. You will have to first figure out how that file came to its place on this server (as part of Umbraco or another software), and then see if its vendor can give you some assistance on troubleshooting. — Lex Li
– Lex Li, Commented Jul 1 at 22:38
Hi @LexLi, thanks for your reply. It helped me figured out what it was, as pcre.dll had the same modification date as other files belonging to the ModSecurity firewall. Not a clue what actually happened to cause the issue, as ModSecurity + OWASP is a default part of the Plesk install and hasn't seen an update in a while, but even then, I'm glad it's resolved for now. — Quan
– Quan, Commented Jul 2 at 6:46

Quan · Accepted Answer · 2025-07-02 06:44:35Z

0

The issue lay in ModSecurity. It was set to "Detection only" with the default OWASP ruleset, but even so, it appeared to throw some kind of error. I have been able to resolve it by setting ModSecurity to Off, or to a different ruleset like Atomic Standard (and then it can be fully on, yielding no problems).

answered Jul 2 at 6:44

Quan

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