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Date: Thu, 31 Dec 2015 06:29:55 +0900
From: Jihyeok Seo <>
Subject: Re: CVE Request: Squashfs 4.2 Race Condition

Privilege boundary crossing does not necessarily happen. However, since unsquashfs is often run with sudo (Squashfs filesystem containing files owned by root), it is a possibility. I do not know if this bug can lead to code execution.

However, firmware upgrade procedures (remote or local) which uses unsquashfs, on devices such as network routers, could be crashed with an untrusted Squashfs filesystem image and lead to denial of service.

> On Dec 31, 2015, at 5:37 AM, wrote:
> Hash: SHA256
>> A malformed Squashfs filesystem can cause a race condition in unsquashfs.
>> This is caused by the decompress thread attempting to access a shared
>> queue, resulting in a SIGSEGV.
>>    struct cache_entry *entry = queue_get(to_deflate);
> Do you have any information about a scenario in which this bug crosses
> a privilege boundary?
> Do you mean that, because of the details of the SIGSEGV, there's a
> reasonable likelihood of code execution when a victim runs unsquashfs
> on an untrusted SquashFS filesystem image?
> Other possibilities in which there could be a CVE ID assigned include:
>  - if the affected unsquashfs code were also available as a library
>    that was used to build a program that was supposed to remain
>    running to handle multiple unsquash operations
>  - if the affected unsquashfs code were also used to support a
>    SquashFS filesystem that was mounted on a system, and an
>    unprivileged user could crash the system by reading from the
>    filesystem
>  - (again for this use of the affected code) if a system exists that
>    automatically mounts SquashFS filesystems found on removable
>    media, and inserting removable media could crash the system
>  - (again for this use of the affected code) maybe a scenario in
>    which the SIGSEGV ultimately leads to disclosure of private data
>    that wasn't contained in the SquashFS filesystem
> - -- 
> CVE assignment team, MITRE CVE Numbering Authority
> M/S M300
> 202 Burlington Road, Bedford, MA 01730 USA
> [ PGP key available through ]
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