CVE-2021-40839

Infinite Loop in rencode

7.5 HighPublic exploitFix available

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.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: None
Availability: High

Exploit likelihood

5.52%Up 4.5 points since Sep 10, 2021

What each source reports

NVD Score used7.5

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.

Record: CVE-2021-40839
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0: 5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness: CWE-835
Updated: 2026-11-02

CVE ListNo score

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.

Record: CVE-2021-40839
Updated: 2026-11-02

EUVDEUVD-2021-0222No score

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.

Record: EUVD-2021-0222
Updated: 2026-11-03

GitHub AdvisoriesGHSA-gh8j-2pgf-x4588.7

Infinite Loop in rencode

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.

Record: GHSA-gh8j-2pgf-x458
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-835
Updated: 2026-11-02

OSVALPINE-CVE-2021-408397.5

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.

Record: ALPINE-CVE-2021-40839
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-03

OSV7.5

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.

Record: CVE-2021-40839
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

Show 5 moreShow less

OSVDEBIAN-CVE-2021-408397.5

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.

Record: DEBIAN-CVE-2021-40839
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVGHSA-gh8j-2pgf-x4588.7

Infinite Loop in rencode

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.

Record: GHSA-gh8j-2pgf-x458
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-835
Updated: 2026-11-02

OSVUBUNTU-CVE-2021-408397.5

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.

Record: UBUNTU-CVE-2021-40839
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVMGASA-2022-0167No score

Updated python-rencode packages fix security vulnerability

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. (CVE-2021-40839)

Record: MGASA-2022-0167
Updated: 2026-11-02

OSVPYSEC-2021-345No score

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.

Record: PYSEC-2021-345
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`rencode` PyPI	through 1.0.6	None known
`py3-rencode` Alpine:v3.17	before 1.0.6-r7	1.0.6-r7
`py3-rencode` Alpine:v3.18	before 1.0.6-r7	1.0.6-r7
`py3-rencode` Alpine:v3.19	before 1.0.6-r7	1.0.6-r7
`py3-rencode` Alpine:v3.20	before 1.0.6-r7	1.0.6-r7
`py3-rencode` Alpine:v3.21	before 1.0.6-r7	1.0.6-r7
`py3-rencode` Alpine:v3.22	before 1.0.6-r7	1.0.6-r7
`py3-rencode` Alpine:v3.23	before 1.0.6-r7	1.0.6-r7
`py3-rencode` Alpine:v3.24	before 1.0.6-r7	1.0.6-r7
`python-rencode` Debian:12	before 1.0.6-2	1.0.6-2

Show 9 moreShow less

Affected packages
Package	Affected	Fixed
`python-rencode` Debian:13	before 1.0.6-2	1.0.6-2
`python-rencode` Debian:14	before 1.0.6-2	1.0.6-2
`rencode` PyPI	through 1.0.6, plus listed versions 1.0.31.0.41.0.5	None known
`python-rencode` Mageia:8	before 1.0.6-2.1.mga8	1.0.6-2.1.mga8
`rencode` PyPI	All versions, plus listed versions 1.0.31.0.41.0.51.0.61.0.71.0.8	None known
`python-rencode` Ubuntu:16.04:LTS	All versions, plus listed versions 1.0.3-1build11.0.3-1build2	None known
`python-rencode` Ubuntu:18.04:LTS	All versions, plus listed versions 1.0.5-1build2	None known
`python-rencode` Ubuntu:20.04:LTS	All versions, plus listed versions 1.0.5-1build41.0.5-1build51.0.5-1.11.0.6-11.0.6-1build1	None known
`python-rencode` Ubuntu:22.04:LTS	All versions, plus listed versions 1.0.6-1build31.0.6-21.0.6-2build1	None known

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
Source	Link	Date
PoC in GitHub	itlabbet/CVE-2021-40839	2021-12-13

History

History
Recorded	Changed	Sources
Nov 3, 2026	affected, aliases, references	OSV
Nov 3, 2026	aliases	EUVD
Nov 2, 2026	first indexed	CVE List, GitHub Advisories, NVD, OSV, PoC in GitHub

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-40839 is a high vulnerability (CVSS 7.5) in Rencode Project Rencode, published September 10, 2021. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 5.52%, the 92nd percentile. Fixed in py3-rencode 1.0.6-r7.

References

Show 14 moreShow less