CVE-2021-43963

An issue was discovered in Couchbase Sync Gateway 2.7.0 through 2.8.2. The bucket credentials used to read and write data in Couchbase Server were insecurely being stored in the metadata within sync documents written to the bucket. Users with read access could use these credentials to obtain write access. (This issue does not affect clusters where Sync Gateway is authenticated with X.509 client certificates. This issue also does not affect clusters where shared bucket access is not enabled on Sync Gateway.)

Published: 2021-12-07 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-43963 is rated Moderate Risk (46.2/100): CVSS High severity, with low exploitation likelihood (EPSS 0.50%). Review affected assets and schedule remediation.

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

Exploit prediction scoring system (EPSS) score for CVE-2021-43963

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 0.24% 0.50% +0.26%
2 2026-02-08 0.33% 0.24% -0.09%
3 2025-11-21 — 0.33% —

Full EPSS history (12 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-43963

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.1 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:L)
A normal user session is enough; they don’t have to be admin.
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:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 5.2 [email protected]
5.5 2.0 MEDIUM
AV:N/AC:L/Au:S/C:P/I:P/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:S)
A single authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.0 4.9 [email protected]

Weakness enumeration for CVE-2021-43963

Affected software / configurations for CVE-2021-43963

Vendor Product Version Raw CPE
couchbase sync_gateway >= 2.7.0, < 2.8.3 cpe:2.3:a:couchbase:sync_gateway:*:*:*:*:*:*:*:*

References for CVE-2021-43963

URL Tags
https://www.couchbase.com/alerts Vendor Advisory
cvelogic Threat Intelligence