How severe is CVE-2021-43557?

CVE-2021-43557 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 high, integrity none, and availability none.

Is CVE-2021-43557 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 15% (96th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-43557?

CVE-2021-43557 affects Apache Apisix. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-43557?

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-2021-43557 published?

CVE-2021-43557 was published on 2021-11-22 and last updated on 2026-06-17.

CVE-2021-43557

CVE-2021-43557 is a high-severity vulnerability in Apache Apisix with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 15% places it in the 96th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-77.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 15% (96th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-77
Affected product: Apache Apisix
Published: 2021-11-22
Last modified: 2026-06-17

Description

The uri-block plugin in Apache APISIX before 2.10.2 uses $request_uri without verification. The $request_uri is the full original request URI without normalization. This makes it possible to construct a URI to bypass the block list on some occasions. For instance, when the block list contains "^/internal/", a URI like `//internal/` can be used to bypass it. Some other plugins also have the same issue. And it may affect the developer's custom plugin.

Frequently asked questions

What is CVE-2021-43557?: The uri-block plugin in Apache APISIX before 2.10.2 uses $request_uri without verification. The $request_uri is the full original request URI without normalization. This makes it possible to construct a URI to bypass the block list on some occasions. For instance, when the block list contains "^/internal/", a URI like `//internal/` can be used to bypass it. Some other plugins also have the same issue. And it may affect the developer's custom plugin.
How severe is CVE-2021-43557?: CVE-2021-43557 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 high, integrity none, and availability none.
Is CVE-2021-43557 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 15% (96th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-43557?: CVE-2021-43557 affects Apache Apisix. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-43557?: 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-2021-43557 published?: CVE-2021-43557 was published on 2021-11-22 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:apache:apisix:*:*:*:*:*:*:*:*

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