1817530 - Frozen `rv:` segment in the User Agent string breaks websites that use a certain anti-spam script

Status: RESOLVED FIXED

(Web Compatibility :: Interventions, defect)

Description

[Andrew Morris]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/110.0

Steps to reproduce:

Open Firefox 110 (desktop). Access a web forum using a certain anti-spam script; in this example, https://www.quatloos.com/Q-Forum/.

Actual results:

The script blocks access, reports "Malformed UA", and reports back the user agent string "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/110.0". Note the mismatch between the "rv" and the Firefox version.

Expected results:

Per the Mozilla documentation (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/User-Agent/Firefox), the UA should be reported with "rv:110.0" to match the Firefox version. Forcing a user-agent string (using the general.useragent.override config key) with "rv:110.0" satisfies the anti-spam script and grants access; clear the key, and it blocks access again. User feedback on the affected forum indicates this started after updating to 110, and is also resolved by downgrading.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Networking: HTTP' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Gregory Pappas [:gregp]]

This is intentional behavior from bug 1805967.

Comment 3

[Dennis Schubert [:denschub]]

ni? myself for investigation here. While it is indeed intentional, our intention is not to break things. Maybe we have to override-override the UA in some cases.

Comment 4

[Masatoshi Kimura [:emk]]

Also should we contact Zaphod?

Comment 5

[Dennis Schubert [:denschub]]

Yeah, I'll try to reach out.

Comment 6

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1805967

Comment 7

[Valentin Gosu [:valentin] (he/him)]

Moving to webcompat::interventions same as regressing bug 1805967.

Comment 8

[Masatoshi Kimura [:emk]]

https://www.quatloos.com/Q-Forum/ no longer blocks Firefox 110.

Comment 9

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1805967

Comment 10

[Masatoshi Kimura [:emk]]

Is this still a problem? The frozen rv:109 hack was removed (bug 1806690).

Comment 11

[:Gijs (he/him)]

(In reply to Masatoshi Kimura [:emk] from comment #10)

Is this still a problem? The frozen rv:109 hack was removed (bug 1806690).

I'm guessing only on ESR.

Comment 12

[Dennis Schubert [:denschub]]

Yeah, we un-froze in bug 1806690. We don't specifically target ESR in interventions at the moment, and I didn't see any significant complaints about this that warrant interventions specific to this. I'll close this as fixed.