Episode 219

Posted on Friday, Feb 16, 2024
This week the Linux kernel project announced they will be assigning their own CVEs so we discuss the possible implications and fallout from such a shift, plus we cover vulnerabilities in the kernel, Glance_store, WebKitGTK, Bind and more.

Show Notes


This week the Linux kernel project announced they will be assigning their own CVEs so we discuss the possible implications and fallout from such a shift, plus we cover vulnerabilities in the kernel, Glance_store, WebKitGTK, Bind and more.

This week in Ubuntu Security Updates

64 unique CVEs addressed

[LSN-0100-1] Linux kernel vulnerability (00:56)

Kernel type 22.04 20.04 18.04 16.04 14.04
aws 100.1 100.1 100.1 100.1
aws-5.15 100.1
aws-5.4 100.1
aws-6.2 100.1
aws-hwe 100.1
azure 100.1 100.1 100.1
azure-4.15 100.1
azure-5.4 100.1
azure-6.2 100.1
gcp 100.1 100.1 100.1
gcp-4.15 100.1
gcp-5.15 100.1
gcp-5.4 100.1
gcp-6.2 100.1
generic-4.15 100.1 100.1
generic-4.4 100.1 100.1
generic-5.15 100.1
generic-5.4 100.1 100.1
gke 100.1 100.1
gke-5.15 100.1
gkeop 100.1
hwe-6.2 100.1
ibm 100.1 100.1
ibm-5.15 100.1
linux 100.1
lowlatency-4.15 100.1 100.1
lowlatency-4.4 100.1 100.1
lowlatency-5.15 100.1
lowlatency-5.4 100.1 100.1

To check your kernel type and Livepatch version, enter this command:

canonical-livepatch status

[USN-6624-1] Linux kernel vulnerabilities

[USN-6625-1] Linux kernel vulnerabilities

[USN-6626-1] Linux kernel vulnerabilities

[USN-6625-2] Linux kernel (GCP) vulnerabilities

[USN-6628-1] Linux kernel (Intel IoTG) vulnerabilities

[USN-6626-2] Linux kernel vulnerabilities

[USN-6608-2] Linux kernel (NVIDIA) vulnerabilities

[USN-6635-1] Linux kernel (GCP) vulnerabilities

[USN-6627-1] libde265 vulnerabilities (04:10)

[USN-6630-1] Glance_store vulnerability (05:26)

  • 1 CVEs addressed in Focal (20.04 LTS), Jammy (22.04 LTS), Mantic (23.10)
  • OpenStack Image Service store library - library for interacting with assets (images) via different storage technologies (local file-system, HTTP, RBD, Swift, S3 and others)
  • S3 backend would log the access_key if logging configured at DEBUG level - any user then able to read the logs could see the access key and hence potentially get access to the S3 bucket (would also need the secret key too and this was never logged so impact minimal)

[USN-6631-1] WebKitGTK vulnerabilities (06:26)

  • 3 CVEs addressed in Jammy (22.04 LTS), Mantic (23.10)
  • Minimal info as with all webkit issues
    • “improved memory handling to fix possible arbitrary code execution when processing crafted web content”
    • “improved access restrictions to fix user fingerprinting from a crafted web page”
    • “improved checks to fix a type confusion issue able to be triggered from crafted web content - possibly exploited in the wild”

[USN-6632-1] OpenSSL vulnerabilities (07:13)

[USN-6633-1] Bind vulnerabilities (07:33)

  • 5 CVEs addressed in Jammy (22.04 LTS), Mantic (23.10)
  • Range of issues including 2 different CPU-based DoS - one in handling of regular DNS queries / responses, the other in DNSSEC - “KeyTrap” - also affects resolvers not just servers (so any client system as well that is doing lookups) - affects the DNSSEC standard itself and hence affects various other implementations as well
  • Attack works by having an attacker create a DNS zone with many RRSIG and DNSKEY records - these contain a cryptographic signature and public key respectively - so when trying to validate the DNSSEC record need both - and so will end up trying every possible RRSIG with every possible DNSKEY to find a match - with no bound on the computation time (and if implemented in a single threaded manner) - can completely DoS the server / client etc.
  • Plus a similar issue in the NSEC3 proof of non-existence in DNSSEC

[USN-6634-1] .NET vulnerabilities (09:47)

  • 2 CVEs addressed in Jammy (22.04 LTS), Mantic (23.10)
  • Updates for dotnet 6, 7 and 8
  • DoS when parsing X509 certificates if using OpenSSL (as is the case in Ubuntu) and a DoS in the SignalR library (allows a server to send asynchronous notifications to client-side web applications) able to be triggered by a malicious client

[USN-6629-1, USN-6629-2] UltraJSON vulnerabilities (10:34)

  • 3 CVEs addressed in Xenial ESM (16.04 ESM), Bionic ESM (18.04 ESM), Focal (20.04 LTS), Jammy (22.04 LTS)
  • Fast JSON encoder/decoder for Python
  • Is actually implemented in C with Python bindings - so has usual issues - UAF, memory corruption, stack buffer overflow

Goings on in Ubuntu Security Community

Linux kernel becomes a CNA (11:25)

  • Earlier this week, Greg Kroah-Hartman (one of the more famous Linux kernel developers - responsible for the various stable kernel trees / releases plus various subsystems within the kernel - also wrote one of the most popular books on Linux Kernel Driver development - even if it is woefully outdated nowadays) announced that the Linux kernel project itself has been accepted as a CNA by MITRE and would start issues CVEs for the vulnerabilities found within the kernel itself

  • Historically the upstream kernel developers and Greg himself have been quite disparaging of the CVE process / ecosystem and essentially saying that CVEs for the kernel are meaningless since that all bugs are potentially security issues and there are so many fixes that go into the kernel of which the security impact is not clear, that the only way to stay secure is to track one of the supported upstream stable kernel trees - otherwise CVEs would be issued for basically every commit that goes into one of the stable trees

    • Whilst in Ubuntu we tend to agree that the only way to maintain a kernel is to use the stable trees (and hence the Ubuntu Kernel team continuously incorporates all the fixes from the upstream stable kernel trees into the different Ubuntu kernels) we still see a lot of value in the CVE ecosystem - and also we do not agree that all fix commits warrant a CVE
  • It was not then surprising to see that in the initial announcement there was a statement that:

    Note, due to the layer at which the Linux kernel is in a system, almost any bug might be exploitable to compromise the security of the kernel, but the possibility of exploitation is often not evident when the bug is fixed. Because of this, the CVE assignment team is overly cautious and assign CVE numbers to any bugfix that they identify.

  • This led many (including us) to fear that the kernel CNA would be issuing an extremely high volume of CVEs which would effectively overwhelm the CVE process and make it unworkable - for instance, LWN calculated that for the 6.1 stable kernel has had over 12,000 fixes applied to it over the past year. So this leaves a huge scope for many CVEs to be possibly assigned - and as a comparison in total across all software / hardware devices etc in 2023 there was 29,000 CVEs assigned. So that could mean the kernel itself would possibly become responsible for at least a quarter of all CVEs in the future.

  • Greg has some prior form in this space as well since in 2019 he gave a talk where he suggested one way the kernel community could help fix the issue of CVEs being erroneously assigned against the kernel would be to start doing exactly this and assigning a CVE for every fix applied to the kernel and hence overwhelm the CVE ecosystem to (in his words) “burn it down”.

  • Also the GSD project (Global Security Database - set up as an alternate / competitor to CVE) was doing exactly this - tracking a huge number of fixes for the stable trees and assigning them GSD IDs - as per https://osv.dev/list?ecosystem=Linux it tracks 13573 issues

  • Thankfully though, this plan seems to have moderated over the past few days - after Greg posted a patch set to the LKML documenting the process, he clarified in a follow-up email that this would not be the case, and instead that CVEs will only be assigned for commits which appear to have a security relevant impact. How they actually do that remains to be seen, and his comment that “we (will) know it when we see it” doesn’t exactly put me at ease (since it is very easy to miss the security implications of any particular commit) at least this helps allay the fears that there would be a tidal wave of CVEs being assigned.

  • One outstanding issue which I directly asked Greg about is how they are actually tracking fixes for CVEs - since in their model, a CVE is equivalent to the commit which fixes the issue - however for lots of existing kernel CVEs that get assigned by other CNAs like Canonical or Red Hat etc, the fix comprises multiple commits

  • Greg says the whole process is quite complex and whilst their existing scripts want a one-to-one mapping from CVEs to commits they do plan to fix this in the future.

  • So will be interesting to see what things they will end up assigning CVEs. Also will be interesting to see how the interaction with security researchers plays out. Since their process is heavily skewed to the CVE corresponding to the fix commit AND they state that this must be in one of the stable trees for a CVE to be assigned, it doesn’t leave a lot of room for responsible disclosure. They do say they can assign a CVE for an issue before it is resolved with a commit to one of the stable trees, but ideally these details would get disclosed to distros and others ahead of the CVE details being released to the public. I also asked Greg about this but am awaiting a response.

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