DescriptionNULL Pointer Dereference allows attackers to cause a denial of service (or application crash). This only applies when lxml is used together with libxml2 2.9.10 through 2.9.14. libxml2 2.9.9 and earlier are not affected. It allows triggering crashes through forged input data, given a vulnerable code sequence in the application. The vulnerability is caused by the iterwalk function (also used by the canonicalize function). Such code shouldn't be in wide-spread use, given that parsing + iterwalk would usually be replaced with the more efficient iterparse function. However, an XML converter that serialises to C14N would also be vulnerable, for example, and there are legitimate use cases for this code sequence. If untrusted input is received (also remotely) and processed via iterwalk function, a crash can be triggered.
SourceCVE (at NVD; CERT, LWN, oss-sec, fulldisc, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs1014766, 1039991

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
libxml2 (PTS)buster2.9.4+dfsg1-7+deb10u4vulnerable
buster (security)2.9.4+dfsg1-7+deb10u6vulnerable
bullseye (security), bullseye2.9.10+dfsg-6.7+deb11u4vulnerable
sid, trixie2.9.14+dfsg-1.3fixed
lxml (PTS)buster, buster (security)4.3.2-1+deb10u4vulnerable
bullseye (security), bullseye4.6.3+dfsg-0.1+deb11u1vulnerable
sid, trixie4.9.3-1fixed

The information below is based on the following data on fixed versions.

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs


[bullseye] - lxml <no-dsa> (Minor issue)
[buster] - lxml <no-dsa> (Minor issue)
[bullseye] - libxml2 <no-dsa> (Minor issue)
[buster] - libxml2 <no-dsa> (Minor issue) (lxml-4.9.1)
Fixed by: (v2.10.0)
Fixed by: (v2.10.0)

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