VulnerabilityPublished 28 Apr 2026Updated 8 May 2026

CVE-2026-33190: github.com/coredns/coredns · CoreDNS has TSIG authentication bypass on DoT, DoH, DoH3, DoQ, and gRPC

Affects github.com/coredns/corednsSource GCVE Database

Authoritative record:CVE-2026-33190· High 8.7

Not known to be exploited · CVSS 8.7 High : upgrade to 1.14.3 soon.

Data as of 27 Oct 2026, 00:07 UTC

CVSS 4.0 base score

8.7High

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 1.14.3

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: None
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 5 May 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade github.com/coredns/coredns to 1.14.3.

Affected software

Product	Affected	Fixed in
Gogithub.com/coredns/coredns	Affected <1.14.3	Fixed in 1.14.3

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### Summary CoreDNS' tsig plugin can be bypassed on non-plain-DNS transports because it trusts the transport writer's TsigStatus() instead of performing verification itself. In the attached PoC, plain DNS/TCP correctly rejects an invalid TSIG (NOTAUTH), while the same invalid-TSIG request is accepted over DoT (tls://) and DoH (https://), allowing a client without the shared secret to satisfy require all. The same bug class affects DoH3, DoQ, and gRPC. ### Details The tsig plugin decides whether an incoming TSIG was valid by consulting w.TsigStatus(): tsigStatus := w.TsigStatus(); if tsigStatus != nil { ... NOTAUTH ... } (plugin/tsig/tsig.go) Two affected transports are shown directly in the PoC: - DoH: DoHWriter.TsigStatus() always returns nil (core/dnsserver/https.go), and the HTTP server passes unpacked DNS messages directly into the plugin chain. - DoT: the TLS server builds a dns.Server without setting TsigSecret (core/dnsserver/server_tls.go), unlike plain DNS/TCP/UDP which sets TsigSecret: s.tsigSecret (core/dnsserver/server.go). The same transport-family bug pattern also appears on other transports: - DoH3 reuses the DoH writer path (core/dnsserver/server_https3.go -> core/dnsserver/https.go), so it inherits the same TsigStatus() == nil behavior. - DoQ uses DoQWriter.TsigStatus() error { return nil } (core/dnsserver/quic.go). - gRPC uses gRPCresponse.TsigStatus() error { return nil } (core/dnsserver/server_grpc.go). The attached PoC was kept deliberately small (baseline TCP+DoT+DoH only) for convenience. ### PoC 1. Adjust COREDNS_BIN in the PoC to point at right path (see the top-level const definitions for tunables as well) 2. Run python3 ./tsig-repro.py 3. Expected output: *** Start CoreDNS *** Corefile: /tmp/vh-f001-tsig-doh-dot-bypass/Corefile Log: /tmp/vh-f001-tsig-doh-dot-bypass/coredns.log *** Baseline (plain TCP) *** no_tsig rcode=5 (expected REFUSED=5) invalid_tsig rcode=9 (expected NOTAUTH=9) *** Candidate (DoT) *** no_tsig rcode=5 (expected REFUSED=5) invalid_tsig rcode=0 ancount=1 (expected NOERROR=0 and ancount>0) *** Candidate (DoH) *** no_tsig http=200 rcode=5 (expected REFUSED=5) invalid_tsig http=200 rcode=0 ancount=1 (expected NOERROR=0 and ancount>0) *** OK *** TSIG bypass reproduced: plain TCP rejects invalid TSIG, while DoT and DoH accept it. Results: /tmp/vh-f001-tsig-doh-dot-bypass/results.json ### Impact Unauthenticated remote clients can bypass TSIG-based authentication/authorization on first-class encrypted transports, enabling access to whatever the deployment intended to restrict behind tsig { require all } (e.g., zone data/privileged queries, etc.).

CWE-287Improper Authentication (opens in a new tab)
Class weaknessLikelihood of exploit: HighOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Architecture and Design · Libraries or Frameworks
Use an authentication framework or library such as the OWASP ESAPI Authentication feature.
OWASP Cheat Sheets
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V2.8.5 (opens in a new tab)
V2.8.4 (opens in a new tab)
V9.2.3 (opens in a new tab)
Attack patterns
Fake the Source of Data (opens in a new tab)
Utilizing REST's Trust in the System Resource to Obtain Sensitive Data (opens in a new tab)
Session Hijacking (opens in a new tab)
Token Impersonation (opens in a new tab)
Upload a Web Shell to a Web Server (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-303Incorrect Implementation of Authentication Algorithm (opens in a new tab)
Base weaknessOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
The requirements for the product dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect.
OWASP Cheat Sheets
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V2.8.5 (opens in a new tab)
V2.8.4 (opens in a new tab)
V9.2.3 (opens in a new tab)
Attack patterns
Reflection Attack in Authentication Protocol (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

WeaknessesCWE-287, CWE-303

Technical details

References

Community reviews

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