How to reproduce the error:
-- A space in my URL will trigger the error.

Observation of the error:
-- It seems to happen suddenly since around 3/10.
---- I did not upgrade my Apache version, but it seems like the -1ubuntu4.27 package was being auto-installed (There are related messages on the /var/log/dpkg.log.).
-- On browser: 403 Forbidden error.
-- On Apache error log: it gets the AH10411: Rewritten query string contains control characters or spaces error.

Potential solution:
I found two references, user @MrWhite suggested using the B flag on RewriteRule. It does work for my server.

My question:
-- Precisely, is it that particular package causing the error?
-- Does this problem only happen to RewriteRule?
-- Is there a universal fix? I mean if I have multiple applications, instead of changing each of their RewriteRule, is it possible to make correction one time and the fix can be applied to the entire server?

Related reference:
-- https://stackoverflow.com/questions/75684314/ah10411-error-managing-spaces-and-20-in-apache-mod-rewrite
-- RewriteRule started returning 403 Forbidden error

  • 1
    I think that the answer is already in your first link which points to security-fix. So I don't know how to flag it. Commented Mar 13, 2023 at 11:45
  • Which directives specifically are you having a problem with? And where exactly? What URLs (and range of characters) are you expecting?
    – MrWhite
    Commented Mar 13, 2023 at 13:01
  • @MrWhite: Thank you for your reply. I would like to first answer your questions: Which directives and where: Sorry if I misunderstand your question please correct me. As far as I can tell it seems any URL that has space and if it is being requested from browser, it will cause the error. If you meant directory path, they are under /var/www/html/. Range of characters: Beside space, I don't know if other characters are having this new problem. I have a feeling that probably more characters are being affected; because I tested some other URL special characters and some of them fail.
    – Chi
    Commented Mar 13, 2023 at 20:52
  • @MrWhite: (Continuing my last message.) Before this problem occurs, there is almost zero problem from all URLs that my server processes. I will need to compare the result of my updated server and my offline server to confirm if some of the URL special characters are being affected by this Apache upgrade. I read your reply from the other question. I have the same doubt, I need more study to find out precisely what kind of security problem does this upgrade package "fix".
    – Chi
    Commented Mar 13, 2023 at 20:57
  • @MrWhite: Based on a search result that I found, I assume before this upgrade, "invalid query string" is being forwarded?
    – Chi
    Commented Mar 13, 2023 at 21:07

2 Answers 2


As pointed out by Rohit Gupta in a comment, there was a change to Apache2 outlined in this git pull request, I just had to change my RewriteRules to include the B and BNP flags.

For example:

RewriteRule ^(.*)$ index.php?q=$1 "[L,QSA,B= ?,BNP]"

The old RewriteRule did not include that B and BNP entries. The BNP may not be necessary for your service. It makes sure to use %20 instead of + for the space (i.e. NP as No Plus).

Make sure you change all the RewriteRule in this way.


The quotation is important in that case because a space delimits parameters by default. In other words:

[L,QSA,B= ?,BNP]

would be viewed as




and obviously Apache2 would fail to load that.


Try replace spaces with +

Add the following after

RewriteBase /
RewriteRule ^(.*)\ (.*)$ /$1+$2 [L,R=301]

in main .htaccess

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