CVE•Published 2021-01-19•Modified 2026-10-14•1 article on news•6 live references•NVD data

CVE-2021-3177Python · Python

Vulnerability data via NVD (ingested)

CVSS v3.1

9.8

CRITICAL

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

EPSS percentile

Exploit Prediction Scoring System · top 2% of all CVEs

Weaknesses (CWE)

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

Description

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.

Timeline

Published 2021-01-19

Modified 2026-10-14

External references

NVD MITRE Exploit-DB Sploitus trickest/cve VulnCheck

Search for exposed instances

Shodan + Censys queries derived from NVD's CPE data. The vuln tag catches assets Shodan has explicitly linked to this CVE; the product / banner fingerprints find exposed instances even when the vuln tag was never applied (which is common).

Shodan · vuln tag19,628 hosts

vuln:CVE-2021-3177

Hosts Shodan has explicitly fingerprinted as vulnerable.

Shodan · product

product:"Python Python"

All exposed Python Python instances — cross-reference with the CVE's affected-version range.

Shodan · banner/body mention

http.html:"Python"

HTTP body or banner mentions "Python" — catches deploys Shodan didn't identify as a product.

More intel sources (5)

Shodan report

vuln:CVE-2021-3177