CVE-2021-43557 | Path traversal in request_uri variable

Exp

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.

Published: 2021-11-22 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-43557 is rated High Exploit Risk (73.7/100): CVSS High severity, with high exploitation likelihood (EPSS 14.59%, 96th percentile). 2 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-43557

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-43557

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 55.26% 14.59% -40.67%
2 2026-06-06 58.26% 55.26% -3.00%
3 2025-12-28 — 58.26% —

Full EPSS history (31 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-43557

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:P/I:N/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-43557

Affected software / configurations for CVE-2021-43557

Vendor Product Version Raw CPE
apache apisix < 2.10.2 cpe:2.3:a:apache:apisix:*:*:*:*:*:*:*:*

References for CVE-2021-43557

URL Tags
http://www.openwall.com/lists/oss-security/2021/11/22/1 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/11/22/2 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2021/11/23/1 Exploit Mailing List Third Party Advisory
https://lists.apache.org/thread/18jyd458ptocr31rnkjs71w4h366mv7h Exploit Mailing List Vendor Advisory
cvelogic Threat Intelligence