CVE-2021-40839

7.5 HIGH 6% exploit odds Fix listed Denial of service Library

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. High risk of service disruption.
Exploit odds: 5.5% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2021-09-10 02:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-06-17 04:07 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 5.5% in the next 30 days (EPSS).
Severity: 7.5 HIGH (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2021-09-10 02:15 UTC
Last modified: 2026-06-17 04:07 UTC
Exploit probability: 5.5% · EPSS, next 30 days
Weakness: CWE-835
Record status: Modified

Affected

Rencode Project Rencode ≤ 1.0.6
Fedoraproject Fedora 34
Fedoraproject Fedora 35

Attack profile CVSS 3.1 · 7.5

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-40839.md and follow it. Check whether this project is affected by CVE-2021-40839. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record