CVE-2021-34739 | Cisco Small Business Series Switches Session Credentials Replay Vulnerability

A vulnerability in the web-based management interface of multiple Cisco Small Business Series Switches could allow an unauthenticated, remote attacker to replay valid user session credentials and gain unauthorized access to the web-based management interface of an affected device. This vulnerability is due to insufficient expiration of session credentials. An attacker could exploit this vulnerability by conducting a man-in-the-middle attack against an affected device to intercept valid session credentials and then replaying the intercepted credentials toward the same device at a later time. A successful exploit could allow the attacker to access the web-based management interface with administrator privileges.

Published: 2021-11-04 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]

Conclusion & alert: CVE-2021-34739 is rated Moderate Risk (59/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.62%). Core evidence: EPSS rose +1.12% over the last day, indicating growing attacker interest. Mandatory action: 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-2021-34739

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 0.50% 1.62% +1.12%
2 2025-11-21 0.70% 0.50% -0.20%
3 2025-11-18 0.70%

Full EPSS history (15 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-34739

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:H/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:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
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.
2.2 5.9 [email protected]
8.1 3.1 HIGH
CVSS:3.1/AV:N/AC:H/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:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
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.
2.2 5.9 [email protected]
6.8 2.0 MEDIUM
AV:N/AC:M/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:M)
Exploitation needs some favorable conditions, but not exceptional ones.
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.
8.6 6.4 [email protected]

Weakness enumeration for CVE-2021-34739

Affected software / configurations for CVE-2021-34739

Vendor Product Version Raw CPE
cisco sf250-24_firmware <= 2.5 cpe:2.3:o:cisco:sf250-24_firmware:*:*:*:*:*:*:*:*
cisco sf250-24p_firmware <= 2.5 cpe:2.3:o:cisco:sf250-24p_firmware:*:*:*:*:*:*:*:*
cisco sf250-48_firmware <= 2.5 cpe:2.3:o:cisco:sf250-48_firmware:*:*:*:*:*:*:*:*
cisco sf250-48hp_firmware <= 2.5 cpe:2.3:o:cisco:sf250-48hp_firmware:*:*:*:*:*:*:*:*
cisco sf250-08_firmware <= 2.5 cpe:2.3:o:cisco:sf250-08_firmware:*:*:*:*:*:*:*:*
cisco sf250-08hp_firmware <= 2.5 cpe:2.3:o:cisco:sf250-08hp_firmware:*:*:*:*:*:*:*:*
cisco sf250-10p_firmware <= 2.5 cpe:2.3:o:cisco:sf250-10p_firmware:*:*:*:*:*:*:*:*
cisco sf250-18_firmware <= 2.5 cpe:2.3:o:cisco:sf250-18_firmware:*:*:*:*:*:*:*:*
cisco sf250-26_firmware <= 2.5 cpe:2.3:o:cisco:sf250-26_firmware:*:*:*:*:*:*:*:*
cisco sf250-26hp_firmware <= 2.5 cpe:2.3:o:cisco:sf250-26hp_firmware:*:*:*:*:*:*:*:*
cisco sf250-26p_firmware <= 2.5 cpe:2.3:o:cisco:sf250-26p_firmware:*:*:*:*:*:*:*:*
cisco sf250-50_firmware <= 2.5 cpe:2.3:o:cisco:sf250-50_firmware:*:*:*:*:*:*:*:*
cisco sf250-50hp_firmware <= 2.5 cpe:2.3:o:cisco:sf250-50hp_firmware:*:*:*:*:*:*:*:*
cisco sf250-50p_firmware <= 2.5 cpe:2.3:o:cisco:sf250-50p_firmware:*:*:*:*:*:*:*:*
cisco sf250x-24_firmware <= 2.5 cpe:2.3:o:cisco:sf250x-24_firmware:*:*:*:*:*:*:*:*
cisco sf250x-24p_firmware <= 2.5 cpe:2.3:o:cisco:sf250x-24p_firmware:*:*:*:*:*:*:*:*
cisco sf250x-48_firmware <= 2.5 cpe:2.3:o:cisco:sf250x-48_firmware:*:*:*:*:*:*:*:*
cisco sf250x-48p_firmware <= 2.5 cpe:2.3:o:cisco:sf250x-48p_firmware:*:*:*:*:*:*:*:*
cisco sf350-08_firmware <= 2.5 cpe:2.3:o:cisco:sf350-08_firmware:*:*:*:*:*:*:*:*
cisco sf350-24_firmware <= 2.5 cpe:2.3:o:cisco:sf350-24_firmware:*:*:*:*:*:*:*:*
cisco sf350-24mp_firmware <= 2.5 cpe:2.3:o:cisco:sf350-24mp_firmware:*:*:*:*:*:*:*:*
cisco sf350-24p_firmware <= 2.5 cpe:2.3:o:cisco:sf350-24p_firmware:*:*:*:*:*:*:*:*
cisco sf350-48_firmware <= 2.5 cpe:2.3:o:cisco:sf350-48_firmware:*:*:*:*:*:*:*:*
cisco sf350-8mp_firmware <= 2.5 cpe:2.3:o:cisco:sf350-8mp_firmware:*:*:*:*:*:*:*:*
cisco sf350-48p_firmware <= 2.5 cpe:2.3:o:cisco:sf350-48p_firmware:*:*:*:*:*:*:*:*
cisco sf352-08_firmware <= 2.5 cpe:2.3:o:cisco:sf352-08_firmware:*:*:*:*:*:*:*:*
cisco sf352-08mp_firmware <= 2.5 cpe:2.3:o:cisco:sf352-08mp_firmware:*:*:*:*:*:*:*:*
cisco sf352-08p_firmware <= 2.5 cpe:2.3:o:cisco:sf352-08p_firmware:*:*:*:*:*:*:*:*
cisco sf350-8pd_firmware <= 2.5 cpe:2.3:o:cisco:sf350-8pd_firmware:*:*:*:*:*:*:*:*
cisco sf350-10_firmware <= 2.5 cpe:2.3:o:cisco:sf350-10_firmware:*:*:*:*:*:*:*:*
cisco sf350-10mp_firmware <= 2.5 cpe:2.3:o:cisco:sf350-10mp_firmware:*:*:*:*:*:*:*:*
cisco sf350-10p_firmware <= 2.5 cpe:2.3:o:cisco:sf350-10p_firmware:*:*:*:*:*:*:*:*
cisco sf350-10sfp_firmware <= 2.5 cpe:2.3:o:cisco:sf350-10sfp_firmware:*:*:*:*:*:*:*:*
cisco sf350-20_firmware <= 2.5 cpe:2.3:o:cisco:sf350-20_firmware:*:*:*:*:*:*:*:*
cisco sf350-28_firmware <= 2.5 cpe:2.3:o:cisco:sf350-28_firmware:*:*:*:*:*:*:*:*
cisco sf350-28mp_firmware <= 2.5 cpe:2.3:o:cisco:sf350-28mp_firmware:*:*:*:*:*:*:*:*
cisco sf350-28p_firmware <= 2.5 cpe:2.3:o:cisco:sf350-28p_firmware:*:*:*:*:*:*:*:*
cisco sf350-28sfp_firmware <= 2.5 cpe:2.3:o:cisco:sf350-28sfp_firmware:*:*:*:*:*:*:*:*
cisco sf350-52_firmware <= 2.5 cpe:2.3:o:cisco:sf350-52_firmware:*:*:*:*:*:*:*:*
cisco sf350-52mp_firmware <= 2.5 cpe:2.3:o:cisco:sf350-52mp_firmware:*:*:*:*:*:*:*:*
cisco sf350-52p_firmware <= 2.5 cpe:2.3:o:cisco:sf350-52p_firmware:*:*:*:*:*:*:*:*
cisco sf355-10p_firmware <= 2.5 cpe:2.3:o:cisco:sf355-10p_firmware:*:*:*:*:*:*:*:*
cisco sg350x-8pmd_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-8pmd_firmware:*:*:*:*:*:*:*:*
cisco sg350x-12pmv_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-12pmv_firmware:*:*:*:*:*:*:*:*
cisco sg350x-24_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-24_firmware:*:*:*:*:*:*:*:*
cisco sg350x-24p_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-24p_firmware:*:*:*:*:*:*:*:*
cisco sg350x-24mp_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-24mp_firmware:*:*:*:*:*:*:*:*
cisco sg350x-24pd_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-24pd_firmware:*:*:*:*:*:*:*:*
cisco sg350x-24pv_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-24pv_firmware:*:*:*:*:*:*:*:*
cisco sg350x-48_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-48_firmware:*:*:*:*:*:*:*:*
cisco sg350x-48p_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-48p_firmware:*:*:*:*:*:*:*:*
cisco sg350x-48mp_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-48mp_firmware:*:*:*:*:*:*:*:*
cisco sg350x-48pv_firmware <= 2.5 cpe:2.3:o:cisco:sg350x-48pv_firmware:*:*:*:*:*:*:*:*
cisco sg350xg-2f10_firmware <= 2.5 cpe:2.3:o:cisco:sg350xg-2f10_firmware:*:*:*:*:*:*:*:*
cisco sg350xg-24f_firmware <= 2.5 cpe:2.3:o:cisco:sg350xg-24f_firmware:*:*:*:*:*:*:*:*
cisco sg350xg-24t_firmware <= 2.5 cpe:2.3:o:cisco:sg350xg-24t_firmware:*:*:*:*:*:*:*:*
cisco sg350xg-48t_firmware <= 2.5 cpe:2.3:o:cisco:sg350xg-48t_firmware:*:*:*:*:*:*:*:*
cisco sx350x-08_firmware <= 2.5 cpe:2.3:o:cisco:sx350x-08_firmware:*:*:*:*:*:*:*:*
cisco sx350x-12_firmware <= 2.5 cpe:2.3:o:cisco:sx350x-12_firmware:*:*:*:*:*:*:*:*
cisco sx350x-24f_firmware <= 2.5 cpe:2.3:o:cisco:sx350x-24f_firmware:*:*:*:*:*:*:*:*
cisco sx350x-24_firmware <= 2.5 cpe:2.3:o:cisco:sx350x-24_firmware:*:*:*:*:*:*:*:*
cisco sx350x-52_firmware <= 2.5 cpe:2.3:o:cisco:sx350x-52_firmware:*:*:*:*:*:*:*:*
cisco sf550x-24_firmware <= 2.5 cpe:2.3:o:cisco:sf550x-24_firmware:*:*:*:*:*:*:*:*
cisco sf550x-24p_firmware <= 2.5 cpe:2.3:o:cisco:sf550x-24p_firmware:*:*:*:*:*:*:*:*
cisco sf550x-24mp_firmware <= 2.5 cpe:2.3:o:cisco:sf550x-24mp_firmware:*:*:*:*:*:*:*:*
cisco sf550x-48_firmware <= 2.5 cpe:2.3:o:cisco:sf550x-48_firmware:*:*:*:*:*:*:*:*
cisco sf550x-48p_firmware <= 2.5 cpe:2.3:o:cisco:sf550x-48p_firmware:*:*:*:*:*:*:*:*
cisco sf550x-48mp_firmware <= 2.5 cpe:2.3:o:cisco:sf550x-48mp_firmware:*:*:*:*:*:*:*:*
cisco sg550x-24_firmware <= 2.5 cpe:2.3:o:cisco:sg550x-24_firmware:*:*:*:*:*:*:*:*
cisco sg550x-24p_firmware <= 2.5 cpe:2.3:o:cisco:sg550x-24p_firmware:*:*:*:*:*:*:*:*
cisco sg550x-24mp_firmware <= 2.5 cpe:2.3:o:cisco:sg550x-24mp_firmware:*:*:*:*:*:*:*:*
cisco sg550x-24mpp_firmware <= 2.5 cpe:2.3:o:cisco:sg550x-24mpp_firmware:*:*:*:*:*:*:*:*
cisco sg550x-48_firmware <= 2.5 cpe:2.3:o:cisco:sg550x-48_firmware:*:*:*:*:*:*:*:*
cisco sg550x-48p_firmware <= 2.5 cpe:2.3:o:cisco:sg550x-48p_firmware:*:*:*:*:*:*:*:*
cisco sg550x-48mp_firmware <= 2.5 cpe:2.3:o:cisco:sg550x-48mp_firmware:*:*:*:*:*:*:*:*
cisco sg550xg-8f8t_firmware <= 2.5 cpe:2.3:o:cisco:sg550xg-8f8t_firmware:*:*:*:*:*:*:*:*
cisco sg550xg-24f_firmware <= 2.5 cpe:2.3:o:cisco:sg550xg-24f_firmware:*:*:*:*:*:*:*:*
cisco sg550xg-24t_firmware <= 2.5 cpe:2.3:o:cisco:sg550xg-24t_firmware:*:*:*:*:*:*:*:*
cisco sg550xg-48t_firmware <= 2.5 cpe:2.3:o:cisco:sg550xg-48t_firmware:*:*:*:*:*:*:*:*
cisco sx550x-12f_firmware <= 2.5 cpe:2.3:o:cisco:sx550x-12f_firmware:*:*:*:*:*:*:*:*

References for CVE-2021-34739

cvelogic Threat Intelligence