CVE-2021-35209

Exp

An issue was discovered in ProxyServlet.java in the /proxy servlet in Zimbra Collaboration Suite 8.8 before 8.8.15 Patch 23 and 9.x before 9.0.0 Patch 16. The value of the X-Host header overwrites the value of the Host header in proxied requests. The value of X-Host header is not checked against the whitelist of hosts Zimbra is allowed to proxy to (the zimbraProxyAllowedDomains setting).

Published: 2021-07-02 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-35209 is rated High Exploit Risk (82.6/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 1.82%). 1 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-2021-35209

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

Exploit prediction scoring system (EPSS) score for CVE-2021-35209

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 2026-05-06 2.45% 1.82% -0.63%
2 2025-12-29 2.66% 2.45% -0.21%
3 2025-12-18 — 2.66% —

Full EPSS history (33 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-35209

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H 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:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P 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:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-35209

Affected software / configurations for CVE-2021-35209

Vendor Product Version Raw CPE
zimbra collaboration >= 8.8, < 8.8.15 cpe:2.3:a:zimbra:collaboration:*:*:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:-:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p1:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p10:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p11:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p12:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p13:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p14:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p15:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p16:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p17:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p18:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p19:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p2:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p3:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p4:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p5:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p6:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p7:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p8:*:*:*:*:*:*
zimbra collaboration 8.8.15 cpe:2.3:a:zimbra:collaboration:8.8.15:p9:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:-:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p1:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p10:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p11:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p12:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p2:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p3:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p4:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p5:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p6:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p7:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p8:*:*:*:*:*:*
zimbra collaboration 9.0.0 cpe:2.3:a:zimbra:collaboration:9.0.0:p9:*:*:*:*:*:*

References for CVE-2021-35209

cvelogic Threat Intelligence