CVE-2021-40839

Name: CVE-2021-40839
Creator: NVD / NIST
Published: 2021-09-10T02:15:07.933+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 5.43%

Last modified Jun 17, 2026

CVE-2021-40839 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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.. EPSS estimates a 5.43% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

7.5/10

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

EPSS Probability

5.43%

91.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-835

Affected Software

Vendor	Product	Versions
Rencode Project	Rencode	<= 1.0.6
Fedoraproject	Fedora	34
Fedoraproject	Fedora	35

References

https://github.com/aresch/rencode/commit/572ff74586d9b1daab904c6f7f7009ce0143bb75Patch, Third Party Advisory
https://github.com/aresch/rencode/pull/29Patch, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BMVQRPDVSVZNGGX57CFKCYT3DEYO4QB6/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MCLETLGVM5DBX6QNHQFW6TWGO5T3DENY/
https://pypi.org/project/rencode/#historyThird Party Advisory
https://seclists.org/fulldisclosure/2021/Sep/16Mailing List, Third Party Advisory
https://security.netapp.com/advisory/ntap-20211008-0001/Third Party Advisory
https://github.com/aresch/rencode/commit/572ff74586d9b1daab904c6f7f7009ce0143bb75Patch, Third Party Advisory
https://github.com/aresch/rencode/pull/29Patch, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BMVQRPDVSVZNGGX57CFKCYT3DEYO4QB6/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MCLETLGVM5DBX6QNHQFW6TWGO5T3DENY/
https://pypi.org/project/rencode/#historyThird Party Advisory
https://seclists.org/fulldisclosure/2021/Sep/16Mailing List, Third Party Advisory
https://security.netapp.com/advisory/ntap-20211008-0001/Third Party Advisory

Timeline

Published: Sep 10, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-40839?

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.

How severe is CVE-2021-40839?

CVE-2021-40839 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 5.43% probability of exploitation in the next 30 days.

How do I fix CVE-2021-40839?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-40839?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST