While most are still digesting the impact of #CloudBleed, @aimaim dropped by the PSXHAX Shoutbox this morning and shared news of this CVE-2017-6074 Linux Kernel DCCP double-free local root vulnerability (Proof-of-Concept by xairy) with us today! 
As was done with CVE-2016-1885, here's to hoping some more PlayStation 4 developers take a peek at it and see what possibilities (if any) it may present.
Until then, some quick observations in the PSXHAX Shoutbox from @xxmcvapourxx:
Hi, This is an announcement about CVE-2017-6074 [1] which is a double-free vulnerability I found in the Linux kernel. It can be exploited to gain kernel code execution from an unprivileged processes.
Fixed on Feb 17, 2017:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=5edabca9d4cff7f1f2b68f0bac55ef99d9798ba4
The oldest version that was checked is 2.6.18 (Sep 2006), which is vulnerable. However, the bug was introduced before that, probably in the first release with DCCP support (2.6.14, Oct 2005).
The kernel needs to be built with CONFIG_IP_DCCP for the vulnerability to be present. A lot of modern distributions enable this option by default.
The bug was found with syzkaller [2].
### Bug details
In the current DCCP implementation an skb for a DCCP_PKT_REQUEST packet is forcibly freed via __kfree_skb in dccp_rcv_state_process if dccp_v6_conn_request successfully returns [3].
However, if IPV6_RECVPKTINFO is set on a socket, the address of the skb is saved to ireq->pktopts and the ref count for skb is incremented in dccp_v6_conn_request [4], so skb is still in use. Nevertheless, it still gets freed in dccp_rcv_state_process.
The fix is to call consume_skb, which accounts for skb->users, instead of doing goto discard and therefore calling __kfree_skb.
To exploit this double-free, it can be turned into a use-after-free:
As this point we have a use-after-free on some_object. An attacker can control what object that would be and overwrite it's content with arbitrary data by using some of the kernel heap spraying techniques.
If the overwritten object has any triggerable function pointers, an attacker gets to execute arbitrary code within the kernel.
I'll publish an exploit in a few days, giving people time to update. New Ubuntu kernels are out so please update as soon as possible.
### Timeline
As was done with CVE-2016-1885, here's to hoping some more PlayStation 4 developers take a peek at it and see what possibilities (if any) it may present.
Until then, some quick observations in the PSXHAX Shoutbox from @xxmcvapourxx:
- kmalloc() <-- dcloser again wow
- but that can cause a lot of issues: https://github.com/fail0verflow/ps4-linux
- config ip dccp ohhhhhhhh wireshark uses it
- can be used on linux
- that DLClose is for IPV6_RECVPKTINFO
- nothing to do with a kernel, if i say
- no its kmalloc
- you just need web crash find that memory
- then find the offsets for vtable and gadgets
Hi, This is an announcement about CVE-2017-6074 [1] which is a double-free vulnerability I found in the Linux kernel. It can be exploited to gain kernel code execution from an unprivileged processes.
Fixed on Feb 17, 2017:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=5edabca9d4cff7f1f2b68f0bac55ef99d9798ba4
The oldest version that was checked is 2.6.18 (Sep 2006), which is vulnerable. However, the bug was introduced before that, probably in the first release with DCCP support (2.6.14, Oct 2005).
The kernel needs to be built with CONFIG_IP_DCCP for the vulnerability to be present. A lot of modern distributions enable this option by default.
The bug was found with syzkaller [2].
### Bug details
In the current DCCP implementation an skb for a DCCP_PKT_REQUEST packet is forcibly freed via __kfree_skb in dccp_rcv_state_process if dccp_v6_conn_request successfully returns [3].
However, if IPV6_RECVPKTINFO is set on a socket, the address of the skb is saved to ireq->pktopts and the ref count for skb is incremented in dccp_v6_conn_request [4], so skb is still in use. Nevertheless, it still gets freed in dccp_rcv_state_process.
The fix is to call consume_skb, which accounts for skb->users, instead of doing goto discard and therefore calling __kfree_skb.
To exploit this double-free, it can be turned into a use-after-free:
Code:
// The first free:
kfree(dccp_skb)
// Another object allocated on the same place as dccp_skb:
some_object = kmalloc()
// The second free, effectively frees some_object
kfree(dccp_skb)If the overwritten object has any triggerable function pointers, an attacker gets to execute arbitrary code within the kernel.
I'll publish an exploit in a few days, giving people time to update. New Ubuntu kernels are out so please update as soon as possible.
### Timeline
- 2017-02-15: Bug reported to security () kernel org
- 2017-02-16: Patch submitted to netdev
- 2017-02-17: Patch committed to mainline kernel
- 2017-02-18: Notification sent to linux-distros
- 2017-02-22: Public announcement
- [1] http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=2017-6074
- [2] https://github.com/google/syzkaller
- [3] http://lxr.free-electrons.com/source/net/dccp/input.c?v=4.9#L606
- [4] http://lxr.free-electrons.com/source/net/dccp/ipv6.c?v=4.9#L351
- [5] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=5edabca9d4cff7f1f2b68f0bac55ef99d9798ba4
