CVE-2020-6817 regular expression denial-of-service (ReDoS) in Bleach
Attackers can cause denial of service in applications using Bleach by exploiting ReDoS in style attribute parsing when specific tags and styles are allowed.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2020-6817?
CVE-2020-6817 is a high-severity denial of service vulnerability in Mozilla Bleach, published on 16 Feb 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
bleach.clean behavior parsing style attributes could result in a regular expression denial of service (ReDoS). Calls to bleach.clean with an allowed tag with an allowed style attribute are vulnerable to ReDoS. For example, bleach.clean(..., attributes={'a': ['style']}).
Weakness: CWE-1333
Which versions are affected by CVE-2020-6817?
3 open source packages ship an affected version, including bleach. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
bleach PyPI | All versions | 3.1.4 |
bleach PyPI | All versions | 3.1.4 |
bleach PyPI | All versions | 3.1.4 |
Products include Mozilla Bleach.
How do I fix CVE-2020-6817?
Upgrade bleach to 3.1.4 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2020-6817 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2020-6817 exists.
Other vulnerabilities in Mozilla Bleach
Sources
Also known as DEBIAN-CVE-2020-6817, DLA-2167-1, GHSA-vqhp-cxgc-6wmm, PYSEC-2020-340, SNYK-PYTHON-BLEACH-561754, UBUNTU-CVE-2020-6817.