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GHSA-3v43-877x-qgmq
No affected components available
CVE-2019-10010
Impact
In league/commonmark 0.18.2 and below, malicious users can insert double-encoded HTML entities into their Markdown like this:
[XSS](javascript:alert%28'XSS'%29)
This library would (correctly) unescape the & entity to & during the parsing step. However, the renderer step would fail to properly re-escape the resulting : string, thus producing the following malicious HTML output:
<p><a href="javascript:alert('XSS')">XSS</a></p>
Browsers would interpret : as a : character and allow the JS to be executed when the link is clicked.
This vulnerability was present in the upstream library this project was forked from and therefore exists in all prior versions of league/commonmark.
Solution
The new 0.18.3 release mirrors the fix made upstream - we no longer attempt to preserve entities when rendering HTML attributes like href, src, title, etc.
The $preserveEntities parameter of Xml::escape() is therefore no longer used internally, so it has been deprecated and marked for removal in the next major release (0.19.0).
Credits
- Mohit Fawaz for identifying the issue
- Sebastiaan Knijnenburg and Ross Tuck for responsibly disclosing/relaying the issue
- John MacFarlane for investigating it and implementing the upstream fix we mirrored here
References
- https://nvd.nist.gov/vuln/detail/CVE-2019-10010
- https://github.com/thephpleague/commonmark/releases/tag/0.18.3
- https://github.com/thephpleague/commonmark/issues/353
- https://github.com/FriendsOfPHP/security-advisories/blob/master/league/commonmark/CVE-2019-10010.yaml
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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