CVE-2021-40839

HIGHNVD 7.57.5—Elevated

7.5

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.

CVSS v3: 7.5
EG Score: 7.5(medium)
EPSS: 95.2%
KEV: Not listed

Published

September 10, 2021

Last Modified

November 21, 2024

References (14)

cve@mitrehttps://github.com/aresch/rencode/commit/572ff74586d9b1daab904c6f7f7009ce0143bb75
cve@mitrehttps://github.com/aresch/rencode/pull/29
cve@mitrehttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BMVQRPDVSVZNGGX57CFKCYT3DEYO4QB6/
cve@mitrehttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MCLETLGVM5DBX6QNHQFW6TWGO5T3DENY/
cve@mitrehttps://pypi.org/project/rencode/#history
cve@mitrehttps://seclists.org/fulldisclosure/2021/Sep/16
cve@mitrehttps://security.netapp.com/advisory/ntap-20211008-0001/
af854a3a-2127-422b-91ae-364da2661108https://github.com/aresch/rencode/commit/572ff74586d9b1daab904c6f7f7009ce0143bb75
af854a3a-2127-422b-91ae-364da2661108https://github.com/aresch/rencode/pull/29
af854a3a-2127-422b-91ae-364da2661108https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BMVQRPDVSVZNGGX57CFKCYT3DEYO4QB6/
af854a3a-2127-422b-91ae-364da2661108https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MCLETLGVM5DBX6QNHQFW6TWGO5T3DENY/
af854a3a-2127-422b-91ae-364da2661108https://pypi.org/project/rencode/#history
af854a3a-2127-422b-91ae-364da2661108https://seclists.org/fulldisclosure/2021/Sep/16
af854a3a-2127-422b-91ae-364da2661108https://security.netapp.com/advisory/ntap-20211008-0001/

Patch Availability(1)

Vendor / Ecosystem	Fixed in / Patch	Released	Source
pip	rencode	—	ghsa

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)

PyPI(1)

Package	Vulnerable range	Fixed in	Dependents
rencode	1.0.3 ... 1.0.8 (6 versions)	572ff74586d9b1daab904c6f7f7009ce0143bb75	—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-835Loop with Unreachable Exit Condition (Infinite Loop)

Data Freshness Timeline

(refreshed 11× in last 7d / 20× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-06-02 20:11 UTCepss_batch
2026-06-02 20:11 UTCepss_batch
2026-06-01 13:50 UTCepss_batch
2026-06-01 13:50 UTCepss_batch
2026-05-31 22:29 UTCepss_batch
2026-05-31 22:29 UTCepss_batch
2026-05-31 00:15 UTCepss_batch
2026-05-31 00:15 UTCepss_batch
2026-05-29 13:42 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-27 13:39 UTCepss_batch
2026-05-27 13:39 UTCepss_batch
2026-05-26 13:42 UTCepss_batch
2026-05-26 13:42 UTCepss_batch
2026-05-26 10:35 UTCEG score recompute
2026-05-26 10:35 UTCGHSA enrichment
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch

Frequently asked(5)

What is CVE-2021-40839?

CVE-2021-40839 is a high vulnerability published on September 10, 2021. 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.

When was CVE-2021-40839 disclosed?

CVE-2021-40839 was first published in the National Vulnerability Database on September 10, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-40839 actively exploited?

CVE-2021-40839 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 95.2% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-40839?

CVE-2021-40839 has a CVSS v3 base score of 7.5 (NVD).

How do I remediate CVE-2021-40839?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-40839, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-40839

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CVE-2021-40839

📅 Published

🔄 Last Modified

🔗 References (14)