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Ubuntu Security Podcast

Episode 159

19 min • 15 maj 2022

Overview

This week we bring you part 2 of our look at the new Ubuntu 22.04 LTS release and what’s in it for security, plus we cover security updates for DPDK, OpenSSL, Cron, RSyslog, Curl and more.

This week in Ubuntu Security Updates

37 unique CVEs addressed

[USN-5401-1] DPDK vulnerabilities [00:54]

  • 2 CVEs addressed in Focal (20.04 LTS), Impish (21.10), Jammy (22.04 LTS)
  • Data-plane development kit (provides TCP offloading to userspace to accelerate package processing workloads)
  • Used by openvswitch for OpenStack software defined networking
  • OOB write due to missing check on queue length in vhost comms - could allow a malicious guest to crash or get code execution on the host
  • Also fixed a possible DoS attack between a malicious vhost-user primary and secondary where the primary can spam the secondary with with a huge number of open file-descriptors which eventually leads the secondary to exhaust it’s fd limit and hence DoS

[USN-5402-1] OpenSSL vulnerabilities [01:36]

  • 4 CVEs addressed in Bionic (18.04 LTS), Focal (20.04 LTS), Impish (21.10), Jammy (22.04 LTS)
  • All 4 affect 22.04 whilst only one affects the older releases - in this case if running 22.04, exposed to 4 vulns whilst for the older releases only 1
    • Would be interesting to try and compare number of CVEs over the lifetime of a piece of software - if always running the latest version do you get exposed to more and more CVEs each time you upgrade? Is it better to stick with older software since the rate of vulns found over time likely decreases as it gets older…
  • Anyway, of these vulns 1 is a memory leak during certificate decoding which could usually affect something like an TLS server which uses client certs for authentication, plus a possible MiTM attack against RC4-MD5, incorrect return code when validating OCSP messages which could cause a user / application to believe was valid when in fact was not plus possible code execution via the c_rehash script through shell-metacharacters - but no privilege escalation so only get whatever privileges the script is executing under (c_rehash is used to create symlinks named as the hashes of certs etc when importing a cert into a cert store so it can then easily be looked up via it’s hash value as the filename)

[USN-5395-2] networkd-dispatcher regression [03:44]

  • 2 CVEs addressed in Bionic (18.04 LTS), Focal (20.04 LTS), Impish (21.10), Jammy (22.04 LTS)
  • Episode 158 - upstream fix contained a small regression where an error would be encountered under certain situations

[USN-5354-2] Twisted vulnerability [04:06]

  • 1 CVEs addressed in Trusty ESM (14.04 ESM), Xenial ESM (16.04 ESM), Jammy (22.04 LTS)
  • Episode 156 - Equivalent update for ESM releases plus latest Ubuntu LTS release

[USN-5403-1] SQLite vulnerability [04:20]

  • 1 CVEs addressed in Bionic (18.04 LTS), Focal (20.04 LTS), Impish (21.10)
  • Crash / possible code execution in CLI client when using a crafted query - upstream dispute this as an actual vuln since if can execute sqlite cli then can already execute arbitrary commands

[USN-5405-1] jbig2dec vulnerabilities [04:40]

  • 2 CVEs addressed in Xenial ESM (16.04 ESM)
  • used in ghostscript, mupdf and others for handling JBIG2 files
  • NULL ptr dereference -> crash -> DoS
  • Heap buffer overflow -> crash / code execution

[USN-5259-2] Cron vulnerabilities [04:58]

  • 4 CVEs addressed in Bionic (18.04 LTS)
  • DoS via a very large crontab file with many many lines or very long lines
  • Ubuntu specific vuln allowing possible privesc from crontab group to root when the crontab package is upgraded via a symlink attack - so in general was a dormant / latent vuln that would only be able to be triggered if a sysadmin manually reinstalled cron or we released a new update 😁 - so fixed now

[USN-5259-3] Cron regression [05:47]

  • 4 CVEs addressed in Xenial ESM (16.04 ESM), Bionic (18.04 LTS)
  • but unfortunately caused a minor regression where some harmless but possibly scary looking error messages would be printed when cron was upgraded - fixed with this further update

[USN-5404-1] Rsyslog vulnerability [05:57]

  • 1 CVEs addressed in Bionic (18.04 LTS), Focal (20.04 LTS), Impish (21.10), Jammy (22.04 LTS)
  • Potential heap buffer overflow in TCP syslog reception - so a malicious host which is logging to a centralized syslog server could possibly crash or get code execution on the server (as the syslog user only)

[USN-5244-2] DBus vulnerability [06:18]

  • 1 CVEs addressed in Bionic (18.04 LTS), Focal (20.04 LTS)
  • Possible UAF when running on a system where multiple usernames are mapped to the same UID - if policy references these usernames, may free it via one username whilst it is still being accessed by the other
  • Not really likely to encounter this setup or be able to easily exploit it

[USN-5179-2] BusyBox vulnerability [07:03]

[USN-5407-1] Cairo vulnerabilities [07:10]

[USN-5408-1] Dnsmasq vulnerability [07:24]

  • 1 CVEs addressed in Trusty ESM (14.04 ESM), Xenial ESM (16.04 ESM), Bionic (18.04 LTS), Focal (20.04 LTS), Impish (21.10), Jammy (22.04 LTS)
  • Heap-based UAF found by oss-fuzz when handling malicious DHCPv6 requests

[USN-5409-1] libsndfile vulnerability [07:46]

  • 1 CVEs addressed in Xenial ESM (16.04 ESM)
  • OOB read in FLAC codec -> crash / possible info leak

[USN-5410-1] NSS vulnerability [07:54]

  • 1 CVEs addressed in Bionic (18.04 LTS), Focal (20.04 LTS)
  • Mishandled ChangeCipherSpec messages in TLS 1.3 - remote client could crash a server by sending multiple of these

[USN-5411-1] Firefox vulnerabilities [08:06]

[USN-5412-1] curl vulnerabilities [08:24]

  • 3 CVEs addressed in Bionic (18.04 LTS), Focal (20.04 LTS), Impish (21.10), Jammy (22.04 LTS)
  • More curl vulns - seems to be more every 5-10 weeks or so lately - fuzzing?
    • logic error on connection reuse could reuse an old connection after parameters had been changed
    • Possible infinite loop when constructing a server’s TLS cert chain -> DoS
    • incorrect handling of %-encoded URL separators - could parse URL wrongly and so end up visiting wrong URL or bypassing access checks / filters etc
  • curl is part of hackerone and has so far paid out $17k USD in bounties
  • Whilst preparing this week’s episode 6 more vulns were announced in curl
  • Interesting twitter thread from curl maintainer on the ratio of vulns which are due to C mistakes vs general programming logic mistakes - general mistakes higher so I assume this is used as an argument as to why implementing such a ubiquitous piece of software in such an unsafe language is “ok” - can’t say I agree
  • Also compared how long it takes to find vulns from C mistakes vs non-C mistakes - non-C mistakes take longer to find, presumably due to lack of good tools for finding them (compared to say UBSan, Coverity etc for finding C specific mistakes)

Goings on in Ubuntu Security Community

What’s new in security in Ubuntu 22.04 LTS (part 2) [11:35]

  • In part 1 we covered new security features in the kernel
  • This week we look at userspace security improvements
    • OpenSSL 3
      • disables a lot of legacy algorithms by default, upstream have a migration guide which explains the main changes from 1.1.1 as well as how to enable the legacy provider if you still require access to them
      • Default security level is still 2 but it now disables (D)TLS 1.2 protocols (and below)
    • openssh 8.9
      • Lots of changes since 8.2 in 20.04 LTS, but in particular has improved handling of FIDO/U2F hardware tokens - openssh in 20.04 LTS first introduced support for FIDO/U2F tokens as 2FA for remote SSH logins - basically would generate a new openssh key where the private half of the key is only accessible with the FIDO/U2F token - this new release brings support for using a PIN with the token and much better improved UX so that users don’t have to keep getting prompted for their PIN each time. Plus supports verifying WebAuthn signatures
    • nftables as default firewall backend
      • firewalling on Linux has 2 components - kernel-space mechanism and userspace tooling to control that
      • traditionally kernel supported iptables (aka xtables - ip,ip6,arp,eb -tables)
      • nftables as introduced into the kernel in 3.13 as a new mechanism to implement network packet classification and handling - aka firewalling etc
      • kernel has 2 mechanisms then - xtables and nftables
      • userspace then has 2 primary tools for handling these - iptables for xtables and nftables (nft) for nftables
      • iptables userspace added a nft backend so existing iptables rules and users would be switched to that automatically - so can still use traditional iptables command to configure firewall rules etc but they will then be loaded into the kernel’s nft backend rather than xtables
      • also has a separate userspace command nft to directly configure nft backend which supports more advanced rule types
      • Need to be careful that all tools which configure firewall rules use the same backend in the kernel otherwise they may conflict and get weird results
    • gcc 11 with improved static analysis via -fanalyzer
      • Double free, UAF, free of non-heap memory, malloc leak, NULL ptr deref, unsafe calls within signal handlers and more
    • bash 5.1 - $SRANDOM vs $RANDOM
      • RANDOM is a psuedo-random number which comes internally from bash and hence is deterministic based on the original seed value
      • SRANDOM is derived from the kernel’s /dev/urandom and hence is not reproducible / deterministic - ie. is actually more truly random
    • Private home directories by default

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