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vulnerability tcp RFC 5961 of linux kernel since v3.2

Tracked by Jolla (In release)

asked 2016-08-19 12:10:10 +0200

cemoi71 gravatar image

updated 2018-05-04 11:48:33 +0200

Hello all

I Don't know if a lots of people already aware about it. Seems not to be after tjc research

shortly on the usenix security conference was reported from a vulnerability on the TCP Protocol RFC 5961.
As i understand This Version is already implemented into the Linux Kernel since V3.6 but not in windows and ios.

this leak give the possibility to someone making an attack of type man in the middle.

Here is a link with more precision:

Seems that already a lot's a people tracked the leak and have a patch for it...

Now comes the question:
Jolla is able to update the kernel? if the patch is ready, that would be nice to have it. One possible workaround has appeared. But may be a workaround a good and certified alternative?

Edit 04.05.2018: Fix is still not done for JP1
When may we expect to have it in our precious one? Does jolla may give a short word about it from their plan?

Have a nice sail

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create (as root) the file /etc/sysctl.d/rfc5961.conf:

net.ipv4.tcp_challenge_ack_limit = 999999999

and reboot. If you do not want to reboot:

sysctl net.ipv4.tcp_challenge_ack_limit=999999999
cy8aer ( 2016-08-19 13:20:39 +0200 )edit

@cy8aer seems to be completely different as what what we can see by all patches referenced on the above link.
i'm definitively not skilled on the business, so that it makes me more cautious about it.
i prefer wait for explanation and confirmation.
And official reaction/bugfix etc.. would help for sure.
Not that i want to ignore your solution and help. I'm just really cautious with this.
Maybe you could convert your remark as answer. That would help by this process of confirmation, explanation (6 validation). Anyway, many thanks for your fast answer.

cemoi71 ( 2016-08-19 15:11:29 +0200 )edit

@cy8aer i can read it, no problem. and like the author notified, that is a workaround, and not the final and well done solution....
Hope that jolla will close the leak when the solution will be provided...

cemoi71 ( 2016-09-01 16:36:51 +0200 )edit

@cemoi71 it is not yet released in kernel-adaptation-sbj- (jolla1 and I doubt it is in

lpr ( 2018-05-03 17:44:27 +0200 )edit

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answered 2016-08-19 15:39:42 +0200

hoschi gravatar image

updated 2016-08-19 15:56:28 +0200

I don't know how to express this better:
Regular unencrypted TCP-Traffic is generally vulernable to the attack as described here, for this reason, encrypted TCP-Traffic is used. So this is not a new security vulnerability, but implementing RFC5961 fully and correctly (as GNU/Linux sadly does) allows for doing an attack in less time.

So RFC5961 makes unencrypted TCP-Traffic needlessly more vulnerable. Don't panic.
// edit: it's even not by itself a man-in-the-middle-attack

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naturally tcp is not encrypted but as i understand it let a opened door to make code injection on strategic and sensitive places which should be not be reached. Which could allowed a man in the middle attack....
then it is indeed a serious vulnerability. relative complex for normal hacker or user. but for really much more skilled people an interesting one (and peanuts for government-like organisation)...

cemoi71 ( 2016-08-19 16:02:21 +0200 )edit

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Arad qorbani ( 2018-11-18 15:18:36 +0200 )edit

answered 2017-06-01 01:31:07 +0200

IZh gravatar image


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you should apply kernel 3.4 patch for jolla1 instead

lpr ( 2017-07-05 16:58:30 +0200 )edit

no patch at all has been applied to kernel-adaptation-sbj...

lpr ( 2018-05-03 18:08:56 +0200 )edit

I think this is helpful for student and easy to Do my Assignment

alexjohn ( 2018-05-05 09:28:31 +0200 )edit

Editing it will help solve the problem maybe but if you can transfer to windows and gain more knowledge about securing your system it will be better I think, and if you have free time try this brain games for adults

adamsnow ( 2019-01-15 06:09:42 +0200 )edit
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Asked: 2016-08-19 12:10:10 +0200

Seen: 1,191 times

Last updated: Oct 27 '18