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PythonApplication

CVE-2021-3177

CRITICAL · 9.8 CVSS v3.1 Published 2021-01-19
Fix available
A fix is available. Upgrade to after 3.9.1 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-120

A fixed-size buffer is filled without checking the length of the incoming data, so it overflows into neighbouring memory. This is the classic overflow attackers use to overwrite return addresses and hijack execution. The fix is strict length checks and safe, bounded string and memory functions.

General guidance for the classic buffer overflow class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
PythonApplication
Affected:>= 3.6.0, <= 3.6.12>= 3.7.0, <= 3.7.9>= 3.8.0, <= 3.8.7>= 3.9.0, <= 3.9.1
FedoraOperating system
Affected:= 32= 33
Debian LinuxOperating system
Affected:= 9.0
Active Iq Unified ManagerApplication
Affected:all versions
Ontap Select Deploy Administration UtilityApplication
Affected:all versions
Communications Cloud Native Core Network Function Cloud Native EnvironmentApplication
Affected:= 22.2.0
Communications Offline Mediation ControllerApplication
Affected:= 12.0.0.3.0
Communications Pricing Design CenterApplication
Affected:= 12.0.0.3.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 3.9.1
Vendor patch bugs.python.org →
Recommended fix High confidence

Python 3.6.13+ / 3.7.10+ / 3.8.8+ / 3.9.2+ (depending on your major.minor version)

  1. Identify the currently installed Python version using: python3 --version or python --version
  2. For Python 3.6.x: Upgrade to Python 3.6.13 or later
  3. For Python 3.7.x: Upgrade to Python 3.7.10 or later
  4. For Python 3.8.x: Upgrade to Python 3.8.8 or later
  5. For Python 3.9.x: Upgrade to Python 3.9.2 or later
  6. Verify the upgrade was successful by running: python3 --version
  7. Test that any code using c_double.from_param with floating-point input works correctly with the new version
Caveat Minor Python version upgrades within the same major.minor branch typically have minimal breaking changes; however, test critical applications to ensure compatibility with the new Python patch release

Generated from the published advisory — verify against the referenced sources before acting.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-3177 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data