Security readout for executives and security teams
Plain-English summary
CVE-2021-34741 is a denial-of-service flaw in Cisco Email Security Appliance. A crafted email can make an affected appliance consume CPU for an extended period, stopping normal email processing. The business risk is mail disruption, delayed communications, and degraded security inspection rather than data theft.
Executive priority
Treat this as a high-priority availability risk for organizations dependent on Cisco ESA for mail flow. It should be remediated through Cisco guidance, especially where email continuity is operationally critical. There is no source-backed evidence here of active exploitation.
Technical view
The flaw is in Cisco AsyncOS email scanning for ESA and is attributed to insufficient validation of incoming emails. It is remotely reachable, requires no authentication or user interaction, and affects availability only. The provided CVSS 3.1 score is 7.5 high with vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
Likely exposure
Organizations using Cisco Email Security Appliance to scan inbound or routed email may be exposed if running affected AsyncOS software. The source bundle does not provide exact affected or fixed version ranges, so exposure must be confirmed against Cisco's advisory and appliance software inventory.
Exploitation context
The provided sources do not indicate CISA KEV listing or active exploitation. Exploitation is described as sending a crafted email through Cisco ESA, causing prolonged CPU exhaustion and denial of service. No confidentiality or integrity impact is stated.
Researcher notes
The record identifies CWE-770 resource exhaustion and insufficient input validation in the email scanning algorithm. The bundle lacks affected version ranges, fixed releases, workaround details, and proof-of-concept evidence. Avoid assuming exploit availability or specific patches beyond Cisco's advisory.
Mitigation direction
- Check Cisco's advisory for affected AsyncOS versions and official remediation guidance.
- Prioritize vendor-recommended AsyncOS updates for internet-facing or high-volume ESA deployments.
- Monitor ESA CPU, message queues, and mail-processing latency for abnormal sustained spikes.
- Review mail continuity plans for delayed or blocked inbound email processing.
- Escalate to Cisco support if fixed-version applicability is unclear.
Validation and detection
- Inventory all Cisco ESA appliances and record AsyncOS versions.
- Compare each appliance version against Cisco's advisory.
- Confirm whether ESA instances process inbound, outbound, or internal relay mail.
- Review monitoring for historical CPU exhaustion and mail queue growth.
- Verify change records show vendor remediation applied where applicable.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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-770: 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 lookupCVE-2021-34741 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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.
CVSS vector scores
1 official scoreWe 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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20211103 Cisco Email Security Appliance Denial of Service VulnerabilityCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Allocation of Resources Without Limits or Throttling
Allocation of Resources Without Limits or Throttling represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.