Investigate libxml2 vulnerabilities patched in USN-4991-1

[flavorjones]

This issue is to drive investigation and potential action around a set of upstream patches that Canonical judged valuable enough to backport to their distributions using a 2.9.10-based version.

References:

• https://ubuntu.com/security/notices/USN-4991-1
• https://ubuntu.com/security/CVE-2017-8872
• https://ubuntu.com/security/CVE-2019-20388
• https://ubuntu.com/security/CVE-2020-24977
• https://ubuntu.com/security/CVE-2021-3517
• https://ubuntu.com/security/CVE-2021-3516
• https://ubuntu.com/security/CVE-2021-3518
• https://ubuntu.com/security/CVE-2021-3537
• https://ubuntu.com/security/CVE-2021-3541

Summary of Analysis

All of the vulnerabilities listed in this USN are addressed in v2.9.11, and are addressed in the vendored version of libxml2 shipped by Nokogiri v1.11.4 and later.

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History of this notication

• 2021-06-17 Issue created after USN was issued
• 2021-06-18 Analysis performed, no action necessary, issue updated and closed.

[flavorjones]

Analysis

CVE-2017-8872

The htmlParseTryOrFinish function in HTMLparser.c in libxml2 2.9.4 allows attackers to cause a denial of service (buffer over-read) or information disclosure.

• permalink: https://ubuntu.com/security/CVE-2017-8872
• report: https://gitlab.gnome.org/GNOME/libxml2/issues/26
• patch: https://gitlab.gnome.org/GNOME/libxml2/commit/123234f2cfcd9e9b9f83047eee1dc17b4c3f4407

This patch first appears in libxml 2.9.9, which makes me wonder why it's listed as part of this USN. There's a side note that might be illuminating: "fix debian used isn't the final upstream fix". Perhaps a conflicting patch was removed and the upstream fix was adopted? In any case, I'm confident this is addressed in the libxml 2.9.12 version currently being vendored in Nokogiri.

CVE-2019-20388

xmlSchemaPreRun in xmlschemas.c in libxml2 2.9.10 allows an xmlSchemaValidateStream memory leak.

• permalink: https://ubuntu.com/security/CVE-2019-20388
• report: https://gitlab.gnome.org/GNOME/libxml2/merge_requests/68
• patch: https://gitlab.gnome.org/GNOME/libxml2/commit/7ffcd44d7e6c46704f8af0321d9314cd26e0e18a

This patch first appears in libxml 2.9.11.

CVE-2020-24977

GNOME project libxml2 v2.9.10 has a global buffer over-read vulnerability in xmlEncodeEntitiesInternal at libxml2/entities.c. The issue has been fixed in commit 50f06b3e.

• permalink: https://ubuntu.com/security/CVE-2020-24977
• report: https://gitlab.gnome.org/GNOME/libxml2/-/issues/178
• patch: https://gitlab.gnome.org/GNOME/libxml2/-/commit/50f06b3efb638efb0abd95dc62dca05ae67882c2

This patch first appears in libxml 2.9.11

CVE-2021-3517

There is a flaw in the xml entity encoding functionality of libxml2 in versions before 2.9.11. An attacker who is able to supply a crafted file to be processed by an application linked with the affected functionality of libxml2 could trigger an out-of-bounds read. The most likely impact of this flaw is to application availability, with some potential impact to confidentiality and integrity if an attacker is able to use memory information to further exploit the application.

• permalink: https://ubuntu.com/security/CVE-2021-3517
• report: https://gitlab.gnome.org/GNOME/libxml2/-/issues/235
• patch: https://gitlab.gnome.org/GNOME/libxml2/-/commit/bf22713507fe1fc3a2c4b525cf0a88c2dc87a3a2

This patch first appears in libxml 2.9.11

CVE-2021-3516

There’s a flaw in libxml2’s xmllint in versions before 2.9.11. An attacker who is able to submit a crafted file to be processed by xmllint could trigger a use-after-free. The greatest impact of this flaw is to confidentiality, integrity, and availability.

• permalink: https://ubuntu.com/security/CVE-2021-3516
• report: https://gitlab.gnome.org/GNOME/libxml2/-/issues/230
• patch: https://gitlab.gnome.org/GNOME/libxml2/-/commit/1358d157d0bd83be1dfe356a69213df9fac0b539

This patch first appears in libxml 2.9.11

CVE-2021-3518

There’s a flaw in libxml2 in versions before 2.9.11. An attacker who is able to submit a crafted file to be processed by an application linked with libxml2 could trigger a use-after-free. The greatest impact from this flaw is to confidentiality, integrity, and availability.

• permalink: https://ubuntu.com/security/CVE-2021-3518
• report: https://gitlab.gnome.org/GNOME/libxml2/-/issues/237
• patch: https://gitlab.gnome.org/GNOME/libxml2/-/commit/1098c30a040e72a4654968547f415be4e4c40fe7

This patch first appears in libxml 2.9.11

CVE-2021-3537

A vulnerability found in libxml2 in versions before 2.9.11 shows that it did not propagate errors while parsing XML mixed content, causing a NULL dereference. If an untrusted XML document was parsed in recovery mode and post-validated, the flaw could be used to crash the application. The highest threat from this vulnerability is to system availability.

• permalink: https://ubuntu.com/security/CVE-2021-3537
• reports:
  • https://gitlab.gnome.org/GNOME/libxml2/-/issues/243
  • https://gitlab.gnome.org/GNOME/libxml2/-/issues/244
  • https://gitlab.gnome.org/GNOME/libxml2/-/issues/245
• patch: https://gitlab.gnome.org/GNOME/libxml2/-/commit/babe75030c7f64a37826bb3342317134568bef61

This patch first appears in libxml 2.9.11

CVE-2021-3541

A flaw was found in libxml2. Exponential entity expansion attack its possible bypassing all existing protection mechanisms and leading to denial of service.

• permalink: https://ubuntu.com/security/CVE-2021-3541
• report: https://gitlab.gnome.org/GNOME/libxml2/-/issues/228 (private as of 2021-06-18)
• patch: https://gitlab.gnome.org/GNOME/libxml2/-/commit/8598060bacada41a0eb09d95c97744ff4e428f8e

This patch first appears in libxml 2.9.11

[flavorjones]

Summary

All of the vulnerabilities listed in this USN are addressed in v2.9.11, and are addressed in the vendored version of libxml2 shipped by Nokogiri v1.11.4 and later.