SIG(0) validation during query flood may lead to undefined behavior
Undefined behavior may result due to a race condition leading to a use-after-free violation. If BIND receives an incoming DNS message signed with SIG(0), it begins work to validate that signature. If, during that validation, the "recursive-clients" limit is reached (as would occur during a query flood), and that same DNS message is discarded per the limit, there is a brief window of time while the SIG(0) validation may attempt to read the now-discarded DNS message. This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1. BIND 9 versions 9.18.28 through 9.18.49 and 9.18.28-S1 through 9.18.49-S1 are NOT affected.
- Published
- May 20, 2026
- Updated
- Sep 1, 2026
- EPSS
- 0.8% · 55th percentile
- CWE
- CWE-362
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Report tools
Action score
23
Monitor
Low priority for now.
- CVSS
- 23 / 40 · 5.9 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.8%
CISA SSVC decision
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- 5.9
- CNA · isc
- 7.5
- 1.6 point gap
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Affected systems
| Vendor | Product | CPE |
|---|---|---|
| isc | bind | cpe:2.3:a:isc:bind |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- isc bind9.20.0 and later · before 9.20.23
- isc bind9.21.0 and later · before 9.21.22
Versions reported by the vendor
Affected version ranges reported by the assigning authority (isc). Independent of NVD's CPE analysis and usually ahead of it.
ISC BIND 9
- 9.20.0 and later · up to and including 9.20.22affected
- 9.21.0 and later · up to and including 9.21.21affected
- 9.20.9-S1 and later · up to and including 9.20.22-S1affected
- 9.18.28 and later · up to and including 9.18.49not affected
- 9.18.28-S1 and later · up to and including 9.18.49-S1not affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Alpine:v3.20 | bind | from 9.20.0 · before 9.18.49-r0 | 9.18.49-r0 |
| Alpine:v3.22 | bind | from 9.20.0 · before 9.20.23-r0 | 9.20.23-r0 |
| Debian:13 | bind9 | before 1:9.20.23-1~deb13u1 | 1:9.20.23-1~deb13u1 |
| Debian:14 | bind9 | before 1:9.20.23-1 | 1:9.20.23-1 |
| openSUSE:Leap 16.0 | bind | before 9.20.23-160000.1.1 | 9.20.23-160000.1.1 |
| openSUSE:Tumbleweed | bind | before 9.20.23-1.1 | 9.20.23-1.1 |
| Red Hat:hummingbird:1 | bind | before 0:9.18.48-1.1.hum1 | 0:9.18.48-1.1.hum1 |
| Red Hat:hummingbird:1 | bind-doc | before 0:9.18.48-1.1.hum1 | 0:9.18.48-1.1.hum1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP7 | bind | before 9.20.23-150700.3.25.1 | 9.20.23-150700.3.25.1 |
| SUSE:Linux Enterprise Server 16.0 | bind | before 9.20.23-160000.1.1 | 9.20.23-160000.1.1 |
Same product
isc: all recordsOther highest-scoring records for the same primary product.
- CVE-2015-5477named in ISC BIND 9.x before 9.9.7-P2 and 9.10.x before 9.10.2-P3 allows remote attackers to cause a denial of service (REQUIRE assertion fa58Plan
- CVE-2016-2776buffer.c in named in ISC BIND 9 before 9.9.9-P3, 9.10.x before 9.10.4-P3, and 9.11.x before 9.11.0rc3 does not properly construct responses,57Plan
- CVE-2016-1286named in ISC BIND 9.x before 9.9.8-P4 and 9.10.x before 9.10.3-P4 allows remote attackers to cause a denial of service (assertion failure an53Plan
- CVE-2020-8625A vulnerability in BIND's GSSAPI security policy negotiation can be targeted by a buffer overflow attack51Plan
- CVE-2020-8617A logic error in code which checks TSIG validity can be used to trigger an assertion failure in tsig.c51Plan
- CVE-2001-0010Buffer overflow in transaction signature (TSIG) handling code in BIND 8 allows remote attackers to gain root privileges.49Plan
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| alpine:bind | 9.18.49-r0 · Alpine:v3.20 | Package registry (OSV) |
| debian:bind9 | 1:9.20.23-1~deb13u1 · Debian:13 | Package registry (OSV) |
| opensuse:bind | 9.20.23-1.1 · openSUSE:Tumbleweed | Package registry (OSV) |
| red hat:bind | 0:9.18.48-1.1.hum1 · Red Hat:hummingbird:1 | Package registry (OSV) |
| red hat:bind-doc | 0:9.18.48-1.1.hum1 · Red Hat:hummingbird:1 | Package registry (OSV) |
| suse:bind | 9.20.23-160000.1.1 · SUSE:Linux Enterprise Server 16.0 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- none
- Integrity
- none
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- None
- Availability impact
- High
Weakness class (CWE)
CWE-362 · Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
—
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for helpChange log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
- downloads.isc.org/isc/bind9/9.20.23
- downloads.isc.org/isc/bind9/9.21.22
- kb.isc.org/docs/cve-2026-5947
- access.redhat.com/errata/RHSA-2026:7412
- access.redhat.com/security/cve/CVE-2026-5947
- bugzilla.redhat.com/show_bug.cgi?id=2479772
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json
Vendor advisories and official records. Exploit/PoC links are deliberately left out.