Security readout for executives and security teams
Plain-English summary
CVE-2019-6477 is a denial-of-service issue in ISC BIND9. A remote client can make a DNS server allocate excessive resources through TCP-pipelined queries, and closing such a connection can leave the server unresponsive. The business impact is DNS instability or outage, not data theft.
Executive priority
Treat this as a high-priority availability risk for DNS infrastructure. It does not indicate confidentiality compromise, but DNS outages can have broad business impact. Patch externally reachable and mission-critical resolvers first, then confirm vendor-managed products are covered.
Technical view
Affected BIND9 versions mishandle resource accounting for TCP-pipelined DNS queries. The tcp-clients limit does not sufficiently bound per-query resource use on one TCP connection. The CVSS 3.1 score is 7.5 because exploitation is network-accessible, unauthenticated, low complexity, and affects availability only.
Likely exposure
Exposure is likely where affected ISC BIND9 releases are reachable over TCP DNS, including recursive, authoritative, or cached-answer deployments. Organizations using vendor distributions or appliances referenced by Synology, F5, Fedora, Debian, or openSUSE should verify their shipped BIND status.
Exploitation context
The provided sources do not show CISA KEV listing or confirmed active exploitation. The issue is still operationally important because DNS services are internet-facing in many environments and outages can disrupt authentication, routing, application access, and customer traffic.
Researcher notes
Evidence supports a resource-exhaustion flaw tied to TCP pipelining and ineffective tcp-clients limiting. The source bundle gives affected version ranges but does not include exploit sightings, exploit code, or a KEV listing. Validate through version and vendor-advisory correlation rather than active probing.
Mitigation direction
- Apply ISC or operating-system vendor updates addressing CVE-2019-6477.
- Check Synology, F5, Fedora, Debian, or openSUSE advisories for product-specific guidance.
- Prioritize externally reachable DNS servers and high-dependency internal resolvers.
- Monitor BIND resource usage and DNS TCP connection behavior until remediated.
- Document any compensating controls if immediate patching is not possible.
Validation and detection
- Inventory DNS servers and products running or bundling ISC BIND9.
- Compare installed BIND versions against the affected ranges in the advisory.
- Confirm vendor package changelogs reference CVE-2019-6477 or the relevant BIND fix.
- Review DNS availability monitoring for intermittent unresponsiveness or resource exhaustion.
- Verify TCP DNS exposure matches intended network architecture.
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.
CVE-2019-6477 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
- https://kb.isc.org/docs/cve-2019-6477CVE reference · x_refsource_CONFIRM
- https://www.synology.com/security/advisory/Synology_SA_19_39CVE reference · x_refsource_CONFIRM
- FEDORA-2019-73a8737068CVE reference · vendor-advisory, x_refsource_FEDORA
- https://support.f5.com/csp/article/K15840535?utm_source=f5support&%3Butm_medium=RSSCVE reference · x_refsource_CONFIRM
- FEDORA-2019-c703d2304aCVE reference · vendor-advisory, x_refsource_FEDORA
- DSA-4689CVE reference · vendor-advisory, x_refsource_DEBIAN
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.