CVE-2021-40839 Infinite Loop in rencode

What is CVE-2021-40839?

CVE-2021-40839 is a high-severity denial of service vulnerability in Fedoraproject Fedora, published on 10 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

The rencode package through 1.0.6 for Python allows an infinite loop in typecode decoding (such as via ;\x2f\x7f), enabling a remote attack that consumes CPU and memory.

Weakness: CWE-835

Which versions are affected by CVE-2021-40839?

3 open source packages ship an affected version, including rencode. It affects 2 products.

Products include Fedoraproject Fedora, Rencode Project Rencode.

How do I fix CVE-2021-40839?

Upgrade to a fixed version.

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-2021-40839 being exploited?

There is no known exploitation of CVE-2021-40839 in the wild and no public exploit code.

Public exploit code: 1 proofs of concept on GitHub.

Other vulnerabilities in Fedoraproject Fedora

• CVE-2024-4577 PHP-CGI OS Command Injection Exploited Critical 9.8
• CVE-2021-39226 Grafana Authentication Bypass Exploited Critical 9.8
• CVE-2019-5544 VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow Exploited Critical 9.8
• CVE-2024-4947 Google Chromium V8 Type Confusion Exploited Critical 9.6
• CVE-2024-4671 Google Chromium Visuals Use-After-Free Exploited Critical 9.6

All Fedoraproject Fedora vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-40839, GHSA-gh8j-2pgf-x458, MGASA-2022-0167, PYSEC-2021-345, UBUNTU-CVE-2021-40839.