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Topic: Environment variables and base64-function

Author

timo

Joined: 03 Jun 2012
Posts: 45
Location: FI, EU

Posted: Thu 07 May '20 17:02 Post subject: Environment variables and base64-function

Reply with quote

I'm using Content Security Policy with nonce.

In conf, I have this line

Code:

Header set Content-Security-Policy "default-src 'self'; script-src 'self' 'nonce-%{UNIQUE_ID}e' 'report-sample'; style-src 'self' 'nonce-%{UNIQUE_ID}e' 'report-sample'; img-src https: data:; media-src https: data:; font-src 'self'; form-action 'self'; child-src https:; report-uri https://ht23.dy.fi/report-uri.php?vhost=default;"

It works, except that requirement for nonce is a base64-string, and as mod_unique_id produces a string in range [A-Za-z0-9@-], that is with extra characters @ and -, CSP occasionally prevents a script or style.

I have tried to apply Apache function "base64" to produce a properly encoded string from UNIQUE_ID,
'nonce-%{base64:%{reqenv:UNIQUE_ID}}' or
'nonce-%{base64:%{UNIQUE_ID}e}' or something like those
but they all fail, either conf syntax check reports

Code:

Unrecognized header format %

, or if it passes after some editing of %-characters, it results something like

Code:

'nonce-(null)'

or a string like

Code:

'nonce-{base64:XrQf8mkxOEdmE553MAbdIgAAAf8}'

What is the correct syntax to apply base64 to the UNIQUE-ID -variable in conf?

James Blond
Moderator

Joined: 19 Jan 2006
Posts: 7371
Location: Germany, Next to Hamburg

Posted: Thu 14 May '20 19:34 Post subject:

You can use Define[1] If you still have a question please ask again. [1] https://httpd.apache.org/docs/2.4/mod/core.html#define

timo

Joined: 03 Jun 2012
Posts: 45
Location: FI, EU

Posted: Thu 14 May '20 19:53 Post subject:

Reply with quote

Thanks for the reply.

Meanwhile, I came up with another solution.

In conf, I have this:

Code:

RequestHeader set CSP-NONCE "expr=%{base64:%{reqenv:UNIQUE_ID}}"

and I set header in php, with this

Code:

$s_Csp_Nonce = $_SERVER["HTTP_CSP_NONCE"];
header("Content-Security-Policy: default-src 'self'; script-src 'self' 'nonce-{$s_Csp_Nonce}' 'report-sample'; style-src 'self' 'nonce-{$s_Csp_Nonce}' 'report-sample'; img-src https: data:; media-src https: data:; font-src 'self'; form-action 'self'; child-src https:; report-uri https://my_url;");

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Topic: Environment variables and base64-function

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