Security readout for executives and security teams
Plain-English summary
This flaw can let malware on an internal host hide outbound communication inside SSL handshake metadata that Cisco filtering products should inspect. The business risk is covert command-and-control or further data exfiltration despite security controls appearing to be in place.
Executive priority
Prioritize remediation where these products protect sensitive networks or enforce egress controls. This is not rated critical, but it weakens a control meant to detect or block covert outbound activity after compromise.
Technical view
CVE-2021-34749 affects SNI request filtering in Cisco WSA, Cisco FTD, and Snort. Inadequate filtering of the SSL handshake can allow unauthenticated remote bypass of filtering and misuse of SSL ClientHello SNI data for external communication from a compromised host.
Likely exposure
Exposure is likely where Cisco WSA, Cisco FTD, or Snort is relied on to inspect or filter outbound SSL/SNI traffic. The bundle does not provide affected version ranges, so teams must confirm against vendor advisories.
Exploitation context
The provided data does not show CISA KEV listing or active exploitation. The scenario requires a compromised host using the filtering gap for outbound communication, so this is mainly a post-compromise control-bypass and exfiltration risk.
Researcher notes
The source description frames data exfiltration through SSL ClientHello misuse, while the CVSS vector lists confidentiality impact as none and integrity as low. Treat that as a scoring-versus-impact ambiguity and rely on vendor guidance for exact affected versions.
Mitigation direction
- Review Cisco advisory cisco-sa-sni-data-exfil-mFgzXqLN for affected releases and fixed software.
- Apply Cisco fixes or vendor-recommended workarounds for WSA, FTD, and Snort where applicable.
- Apply Debian Snort updates DLA 3317-1 or DSA-5354 where Debian packages are in use.
- Review outbound SSL/SNI monitoring assumptions for hosts with sensitive data access.
Validation and detection
- Inventory Cisco WSA, Cisco FTD, and Snort deployments handling outbound SSL/SNI traffic.
- Compare installed versions and packages with the Cisco and Debian advisories.
- Confirm patched Snort packages are deployed on Debian systems where applicable.
- Review security logs for unusual outbound SNI patterns from high-risk hosts.
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-200: Information exposure and cloud metadata lookup
Information exposure and SSRF weaknesses can make discovery, cloud metadata, and credential material review relevant. 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-2021-34749 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
- Medium
- CVSS
- 5.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
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:C/C:N/I:L/A:N3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.8MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20210818 Multiple Cisco Products Server Name Identification Data Exfiltration VulnerabilityCVE reference · vendor-advisory
- [debian-lts-announce] 20230210 [SECURITY] [DLA 3317-1] snort security updateCVE reference · mailing-list
- DSA-5354CVE reference · vendor-advisory
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.
Exposure of Sensitive Information to an Unauthorized Actor
Exposure of Sensitive Information to an Unauthorized Actor represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.