CVE-2020-28493 is a medium-severity (CVSS 5.3) Uncontrolled Resource Consumption vulnerability in jinja2. 1 public exploit reference exists, so weaponization risk is real. A fix is available for jinja2 — see the affected versions and patch details below.
Regular Expression Denial of Service (ReDoS) in Jinja2
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-28493 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
jinja2Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
This affects the package jinja2 from 0.0.0 and before 2.11.3. The ReDoS vulnerability is mainly due to the _punctuation_re regex operator and its use of multiple wildcards. The last wildcard is the most exploitable as it searches for trailing punctuation. This issue can be mitigated by Markdown to format user content instead of the urlize filter, or by implementing request timeouts and limiting process memory.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | jinja2 | all versions | 2.11.3pip install --upgrade 'jinja2==2.11.3' |
Affected Products
fedorafedoraprojectjinjapalletsprojectsResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jinja2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update jinja2 to 2.11.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-28493 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This flaw is out of support scope for the following products: * Red Hat Enterprise Linux 6 * Red Hat Enterprise Linux 7 * Red Hat Ceph Storage 2 To learn more about Red Hat Enterprise Linux support scopes, please see https://access.redhat.com/support/policy/updates/errata/ In Red Hat OpenStack Platform, because…
If using the jinja2 library as a developer, this flaw can be mitigated by not using the vulnerable urlize() filter, and instead, using Markdown to format user content.Source: Red Hat security advisory for CVE-2020-28493 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 8 | python27:2.7-8050020210811095446.3e7ace8b | RHSA-2021:4151 |
| Red Hat Enterprise Linux 8 | python-jinja2-0:2.10.1-3.el8 | RHSA-2021:4161 |
| Red Hat Enterprise Linux 8 | python38:3.8-8050020210811101222.e3d35cca | RHSA-2021:4162 |
| Red Hat Software Collections for Red Hat Enterprise Linux 7 | python27-babel-0:0.9.6-10.el7 | RHSA-2021:3252 |
| Red Hat Software Collections for Red Hat Enterprise Linux 7 | rh-python38-babel-0:2.7.0-12.el7 | RHSA-2021:3254 |
Frequently Asked Questions
Is CVE-2020-28493 in your dependencies?
Find it across PyPI, including transitive dependencies.