CVE-2021-3177

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2022-05-24. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 3 sources updated this weekElevated
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 19%CVSS: 9.8Exploit: NoneExposed: 0

A fix is available — apply it.

Python 3.x through 3.9.1 has a buffer overflow in PyCArg_repr in _ctypes/callproc.c, which may lead to remote code execution in certain Python applications that accept floating-point numbers as untrusted input, as demonstrated by a 1e300 argument to c_double.from_param. This occurs because sprintf is used unsafely.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
—
EPSS
97.0%
KEV
Not listed

Published

January 19, 2021

Last Modified

December 18, 2025

Advisory Details (10)

Auto-updated May 24, 2026
Patch available. Sources: github_pr.
generic

[SECURITY] Fedora 32 Update: python3.10-3.10.0~a5-1.fc32 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FPE7SMXYUIWPOIZV4DQYXODRXMFX3C5E/
generic

[SECURITY] Fedora 32 Update: python37-3.7.10-1.fc32 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FONHJIOZOFD7CD35KZL6SVBUTMBPGZGA/
generic

[SECURITY] Fedora 33 Update: mingw-python3-3.9.1-2.fc33 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CCFZMVRQUKCBQIG5F2CBVADK63NFSE4A/
generic

[SECURITY] Fedora 32 Update: mingw-python3-3.8.3-8.fc32 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BRHOCQYX3QLDGDQGTWQAUUT2GGIZCZUO/
generic Patch Available

[SECURITY] [DLA 3432-1] python2.7 security update

https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
generic Patch Available

[SECURITY] [DLA 2919-1] python2.7 security update

https://lists.debian.org/debian-lts-announce/2022/02/msg00013.html
generic Patch Available

[SECURITY] [DLA 2619-1] python3.5 security update

https://lists.debian.org/debian-lts-announce/2021/04/msg00005.html
generic
https://lists.apache.org/thread.html/rf9fa47ab66495c78bb4120b0754dd9531ca2ff0430f6685ac9b07772%40%3Cdev.mina.apache.org%3E
github_pr

closes bpo-42938: Replace snprintf with Python unicode formatting in ctypes param reprs.

Fix merged in python/cpython PR #24239 on 2021-01-18 — awaiting tagged release

https://github.com/python/cpython/pull/24239
generic

Issue 42938: [security][CVE-2021-3177] ctypes double representation BoF - Python tracker

https://bugs.python.org/issue42938

Vendor Advisories for CVE-2021-3177(3)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(11)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntupython3.5-venv (3.5.2-2ubuntu0~16.04.13) @ xenial2026-05-26ubuntu
ubuntupython2.7-minimal (2.7.12-1ubuntu0~16.04.18) @ xenial2026-05-26ubuntu
ubuntupython2.7-minimal (2.7.18-1~20.04.1) @ focal2026-05-26ubuntu
ubuntupython3.9-venv (3.9.5-3ubuntu0~20.04.1+esm2) @ focal2026-05-26ubuntu
ubuntupython2.7-minimal (2.7.6-8ubuntu0.6+esm10) @ trusty2026-05-26ubuntu
redhatpython-0:2.7.5-92.el7_92022-06-28redhat
redhatrh-python38-python-urllib3-0:1.25.7-7.el72021-08-24redhat
redhatpython27-python-pygments-0:1.5-5.el72021-08-24redhat
redhatpython27:2.7-8040020210122160212.cdb2db542021-05-18redhat
redhatpython38:3.8-8040020210128125034.b1b639b62021-05-18redhat
redhatpython3-0:3.6.8-37.el82021-05-18redhat

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.

Weakness Classification(1)

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

Additional Vendor Advisories

(9)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 12× in last 7d / 45× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-22 22:47 UTCEG score recompute
  2. 2026-07-22 14:06 UTCEPSS rescore
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  8. 2026-07-01 10:48 UTCOSV refresh
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  37. 2026-06-13 16:13 UTCOSV refresh
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  68. 2026-05-26 22:01 UTCEG score recompute
  69. 2026-05-26 22:01 UTCVendor advisory
  70. 2026-05-26 22:01 UTCGHSA enrichment
  71. 2026-05-26 07:17 UTCEPSS rescore
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Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-3177?
CVE-2021-3177 is a critical vulnerability published on January 19, 2021. Python 3.x through 3.9.1 has a buffer overflow in PyCArgrepr in ctypes/callproc.c, which may lead to remote code execution in certain Python applications that accept floating-point numbers as untrusted input, as demonstrated by a 1e300 argument to cdouble.fromparam. This occurs because sprintf is…
When was CVE-2021-3177 disclosed?
CVE-2021-3177 was first published in the National Vulnerability Database on January 19, 2021, with the most recent update on December 18, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-3177 actively exploited?
CVE-2021-3177 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 97.0% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-3177?
CVE-2021-3177 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-3177?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-3177, 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.

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