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CVE-2021-3967

28
FAUCET Score

CVE-2021-3967 is an improper access control vulnerability affecting Zulip versions prior to 4.10. This flaw allows an authenticated attacker to achieve high impact on confidentiality, integrity, and availability of the system. Despite its high CVSS score of 8.8, there is currently no evidence of active exploitation, publicly available exploit code, or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
< 4.10CPE matchmatch criteria
cpe:2.3:a:zulip:zulip:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

4.1MEDIUM

CVSS:3.0/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:L

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
HIGH
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
LOW
Exploitability Score
0.7
Impact Score
3.4
CvssVersion
3.0

Exploit Intelligence

EPSS Score
0.84%
Probability of exploitation in next 30 days
EPSS Percentile
54.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0084 is in the 49th percentile among its peer group of 17,829 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.3 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

github_advisorypatch availablevia nvd_reference
View patch

References

github.com / zulip/zulip/commit/d5db254ca8167995a1654d1c45ffc74b2fade39a
PatchThird Party Advisory
huntr.dev / bounties/2928a625-0467-4a0a-b4e2-e27322786686
ExploitThird Party Advisory