How severe is CVE-2021-3116?

CVE-2021-3116 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-3116?

CVE-2021-3116 affects the following packages: proxy-py (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2021-3116?

Update proxy-py to 2.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3116 is resolved across your whole dependency graph.

How do I detect CVE-2021-3116 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for proxy-py, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-3116 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2021-3116 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-3116, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-3116?

CVE-2021-3116 has an EPSS (Exploit Prediction Scoring System) score of 1.7%, placing it in the 77th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-3116?

CVE-2021-3116 is classified as CWE-697 (CWE-697). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Is there exploit tooling available for CVE-2021-3116?

2 Metasploit modules reference CVE-2021-3116, which lowers the barrier to weaponization. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-3116 published, and has it been updated?

CVE-2021-3116 was published on January 11, 2021 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2021-3116 — proxy-py

HIGHFix: abhinavsingh/proxy.py#482

CVE-2021-3116 is a high-severity (CVSS 7.5) CWE-697 vulnerability in proxy-py. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for proxy-py — see the affected versions and patch details below.

Logic error in authentication in proxy.py

Also known asGHSA-cmc7-mfmr-xqrxPYSEC-2021-46

Published

Jan 11, 2021

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 31, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.7%probability of exploitation in next 30 days

Lower Risk+0.02%

Lower risk than most CVEs77th percentile — riskier than 77% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐍proxy-py

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

before_upstream_connection in AuthPlugin in http/proxy/auth.py in proxy.py before 2.3.1 accepts incorrect Proxy-Authorization header data because of a boolean confusion (and versus or).

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`proxy-py`	all versions	2.3.1`pip install --upgrade 'proxy-py==2.3.1'`

Affected Products

1 product · 1 configurations

Application

proxy.pyproxy.py_project

< 2.3.1

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

before_upstream_connection in AuthPlugin in http/proxy/auth.py in proxy.…

cardaci.xyzNVDJan 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for proxy-py, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update proxy-py to 2.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3116 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

before_upstream_connection in AuthPlugin in http/proxy/auth.py in proxy.py before 2.3.1 accepts incorrect Proxy-Authorization header data because of a boolean confusion (and versus or).

O3 Security · Impact-Aware SCA

Is CVE-2021-3116 in your dependencies?

Find it across PyPI, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

7.5/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Raw vector

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

CWE Classification

Weaponization

OpenSSF Scorecard

Package health score

proxy.py

4.1/10

Code-Review0/10

Maintained2/10

Branch-ProtectionN/A

Assessed Oct 26, 2026

Timeline

Disclosed

Jan 11, 2021

First exploit

Jan 14, 2021

3 days after disclosure — rapid exploitation

Last updated

Oct 20, 2026

Identifiers

CVE-2021-3116

GHSA-cmc7-mfmr-xqrx

PYSEC-2021-46

References

Advisorynvd.nist.gov · CVE 2021 3116 Advisorygithub.com · GHSA cmc7 mfmr xqrx Fixgithub.com · 9b00093288237f5073c403f2c4f62acfdfa8ed46 Webgithub.com Webgithub.com · bff171ec26d826ae1d22d2466eaf9d8bdbf059d3 Webcardaci.xyz · proxy.py 2.3.0 broken basic authentication Webgithub.com · PYSEC 2021 46.yaml Packagepypi.org · 2.3.1 Packagegithub.com · proxy.py Evidencecardaci.xyz · proxy.py 2.3.0 broken basic authentication

Related vulnerabilities

This CVE is high severity; 3 of 8 other CVEs with CWE-697 are rated as high or higher (top: critical).

CVE-2026-90711CVE-2026-101912CVE-2026-101913CVE-2026-79913CVE-2026-61795CVE-2026-61672CVE-2026-55771CVE-2026-59890Browse all CWE-697

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 20, 2026

CVE-2021-3116 — proxy-py

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2021-3116 in your dependencies?