How severe is CVE-2021-3116?

CVE-2021-3116 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2021-3116 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3116?

CVE-2021-3116 affects Proxy.py Project Proxy.py. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-3116?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-3116 published?

CVE-2021-3116 was published on 2021-01-11 and last updated on 2026-06-17.

CVE-2021-3116

CVE-2021-3116 is a high-severity vulnerability in Proxy.py Project Proxy.py with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-697.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 2% (74th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-697
Affected product: Proxy.py Project Proxy.py
Published: 2021-01-11
Last modified: 2026-06-17

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).

Frequently asked questions

What is CVE-2021-3116?: 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).
How severe is CVE-2021-3116?: CVE-2021-3116 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2021-3116 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3116?: CVE-2021-3116 affects Proxy.py Project Proxy.py. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-3116?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-3116 published?: CVE-2021-3116 was published on 2021-01-11 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:proxy.py_project:proxy.py:*:*:*:*:*:*:*:*

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