LiveActive security incident?Get immediate response
CVE Record

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.

HighCVSS 8.1Not KEV-listedUpdated
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

Cisco Small Business Smart and Managed Switches may let an attacker reuse captured web management session credentials. If an administrator session is intercepted, the attacker could later access the same switch management interface with administrator privileges. The sources do not show CISA KEV listing or active exploitation.

Executive priority

Treat this as high priority for environments using affected Cisco small business switches, especially if management interfaces are broadly reachable. The main business risk is unauthorized administrative control of network infrastructure, but exploitation requires a captured valid session.

Technical view

CVE-2021-34739 is a CWE-613 session expiration flaw in Cisco Small Business Series switch web management. CVSS 3.1 score is 8.1 high, with network attack vector and high confidentiality, integrity, and availability impact. Exploitation requires a man-in-the-middle position to capture valid session credentials before replaying them.

Likely exposure

Exposure is most likely where Cisco Small Business Smart or Managed Switch web management is reachable from untrusted networks, shared networks, or paths where traffic interception is plausible. The provided bundle does not identify exact affected versions or CPEs.

Exploitation context

The cited description requires interception of a valid user session, then later replay against the same device. That raises attacker complexity compared with direct remote exploitation, but successful compromise could provide administrator-level management access. No provided source confirms active exploitation.

Researcher notes

Evidence supports a session credential replay issue caused by insufficient session expiration. The source bundle lacks affected version ranges, CPEs, patch names, and exploit-in-the-wild confirmation. Avoid assuming broader Cisco product impact beyond the listed Small Business Smart and Managed Switches.

Mitigation direction

  • Identify Cisco Small Business Smart and Managed Switches in the environment.
  • Check the Cisco advisory for affected releases, fixed software, and official workarounds.
  • Restrict web management access to trusted administrative networks only.
  • Disable external exposure of switch management interfaces where possible.
  • Invalidate active sessions after remediation if the platform supports it.
  • Monitor management logins and configuration changes for anomalies.

Validation and detection

  • Inventory switch models and software versions against Cisco advisory guidance.
  • Confirm management interfaces are not reachable from the internet.
  • Review network paths where administrator sessions could be intercepted.
  • Check logs for unexpected administrator access or configuration changes.
  • Verify session handling after applying vendor-recommended updates.
Prepared
Confidence
medium
Sources
3

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-613: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-34739 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
8.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

8.1High
CVSS 3.1 vector shape for CVE-2021-34739Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
CiscoCisco Small Business Smart and Managed Switchesn/aListed
Weakness

CWE details

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-613 · source CWE mapping

Insufficient Session Expiration

Insufficient Session Expiration represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.