lxml/lxml: NULL Pointer Dereference
CVE-2022-2309 is a high-severity NULL pointer dereference vulnerability in lxml/lxml from Lxml, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 4.9.1 as the first without the flaw, so updating lxml/lxml to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 2.45% chance of exploitation within 30 days, higher than 85% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update lxml/lxml to 4.9.1 or a later version.
- Update Lxml to 4.9.1 or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Lxml | lxml/lxml | before 4.9.1 | 4.9.1 |
| Lxml | Lxml | before 4.9.1 | 4.9.1 |
| Fedora Project | Fedora | 36; 37 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | NVD |
| CVSS 3.0 | 5.3 | Medium | CNA (huntr.dev) |
| CVSS 2.0 | 5.0 | Medium | NVD |
Official description
NULL 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: NULL Pointer Dereference
The product dereferences a pointer that it expects to be valid but is NULL.
How developers prevent this class of flaw
- For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished.
- Select a programming language that is not susceptible to these issues.
- Check the results of all functions that return a value and verify that the value is non-null before acting upon it.
Timeline
- CVE record published.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- github.com/lxml/lxml/commit/86368e9cf70a0ad23cccd5ee32de847149af0c6fThird Party Advisory
- huntr.dev/bounties/8264e74f-edda-4c40-9956-49de635105baExploit, Issue Tracking, Third Party Advisory
Third-party and government advisories
- security.gentoo.org/glsa/202208-06Third Party Advisory
- security.netapp.com/advisory/ntap-20220915-0006/Third Party Advisory
Other references
Recent NULL Pointer Dereference vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
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