HOMEVULNERABILITIESCVE-2021-3177
CRITICAL

CVE-2021-3177

CWE-120Published: January 19, 2021· Updated: Jun 17, 2026

9.8
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-3177 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors & Products

Debian1 product(s)
debian linux
Fedora1 product(s)
fedora
netapp2 product(s)
active iq unified managerontap select deploy administration utility
Oracle5 product(s)
communications cloud native core network function cloud native environmentcommunications offline mediation controllercommunications pricing design centerenterprise manager ops centerzfs storage appliance kit
Python1 product(s)
python
Source: NVD CPE · 11 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://bugs.python.org/issue42938
PATCHhttps://github.com/python/cpython/pull/24239
PATCHhttps://python-security.readthedocs.io/vuln/ctypes-buffer-overflow-pycarg_repr.html
PATCHhttps://www.oracle.com//security-alerts/cpujul2021.html
PATCHhttps://www.oracle.com/security-alerts/cpujan2022.html
PATCHhttps://www.oracle.com/security-alerts/cpujul2022.html
PATCHhttps://www.oracle.com/security-alerts/cpuoct2021.html
PATCHhttps://bugs.python.org/issue42938
PATCHhttps://github.com/python/cpython/pull/24239
PATCHhttps://python-security.readthedocs.io/vuln/ctypes-buffer-overflow-pycarg_repr.html
PATCHhttps://www.oracle.com//security-alerts/cpujul2021.html
PATCHhttps://www.oracle.com/security-alerts/cpujan2022.html
PATCHhttps://www.oracle.com/security-alerts/cpujul2022.html
PATCHhttps://www.oracle.com/security-alerts/cpuoct2021.html
ADVISORYhttps://lists.debian.org/debian-lts-announce/2021/04/msg00005.html
ADVISORYhttps://lists.debian.org/debian-lts-announce/2022/02/msg00013.html
ADVISORYhttps://news.ycombinator.com/item?id=26185005
ADVISORYhttps://security.gentoo.org/glsa/202101-18
ADVISORYhttps://security.netapp.com/advisory/ntap-20210226-0003/
ADVISORYhttps://lists.debian.org/debian-lts-announce/2021/04/msg00005.html
ADVISORYhttps://lists.debian.org/debian-lts-announce/2022/02/msg00013.html
ADVISORYhttps://news.ycombinator.com/item?id=26185005
ADVISORYhttps://security.gentoo.org/glsa/202101-18
ADVISORYhttps://security.netapp.com/advisory/ntap-20210226-0003/

All References (56)

→
https://bugs.python.org/issue42938Exploit · Issue Tracking · Patch · Vendor Advisory
→
https://github.com/python/cpython/pull/24239Patch · Third Party Advisory
→
https://lists.apache.org/thread.html/rf9fa47ab66495c78bb4120b0754dd9531ca2ff0430f6685ac9b07772%40%3Cdev.mina.apache.org%3E
→
https://lists.debian.org/debian-lts-announce/2021/04/msg00005.htmlMailing List · Third Party Advisory
→
https://lists.debian.org/debian-lts-announce/2022/02/msg00013.htmlMailing List · Third Party Advisory
→
https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BRHOCQYX3QLDGDQGTWQAUUT2GGIZCZUO/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CCFZMVRQUKCBQIG5F2CBVADK63NFSE4A/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FONHJIOZOFD7CD35KZL6SVBUTMBPGZGA/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FPE7SMXYUIWPOIZV4DQYXODRXMFX3C5E/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/HCQTCSP6SCVIYNIRUJC5X7YBVUHPLSC4/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MGSV6BJQLRQ6RKVUXK7JGU7TP4QFGQXC/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MP572OLHMS7MZO4KUPSCIMSZIA5IZZ62/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NODWHDIFBQE5RU5PUWUVE47JOT5VCMJ2/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NQPARTLNSFQVMMQHPNBFOCOZOO3TMQNA/

Quick Facts

CVE IDCVE-2021-3177
CVSS Score9.8 / 10
SeverityCRITICAL
WeaknessCWE-120
CISA KEVNo
Affected5 vendor(s)
PublishedJan 19, 2021

Related CVEs (CWE-120)

CVE-2008-3496
10.0
CVE-2010-10016
10.0
CVE-1999-0385
10.0
CVE-1999-1237
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CVE-2001-0191
10.0
CVE-2025-9962
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Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-3177 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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