VulnerabilityPublished 28 Apr 2026Updated 8 May 2026

CVE-2026-35579: github.com/coredns/coredns · CoreDNS has TSIG authentication bypass on gRPC and QUIC transports

Affects github.com/coredns/corednsSource GCVE Database

Not known to be exploited · CVSS 7.5 High : upgrade to 1.14.3 soon.

Data as of 27 Oct 2026, 00:07 UTC

CVSS 3.1 base score

7.5High

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

Patch: Available – fixed in 1.14.3

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, 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: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Apr 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 The gRPC, QUIC, DoH, and DoH3 transports in CoreDNS incorrectly handle TSIG authentication. For gRPC and QUIC, CoreDNS checks whether the TSIG key name exists in the config, but does not actually verify the TSIG HMAC. If the key name matches, `tsigStatus` remains nil and the tsig plugin treats the request as "verified". For DoH and DoH3, the issue is worse: TSIG is not verified at all. The DoH response writer has `TsigStatus()` hardcoded to return nil, so any request containing a TSIG record is treated as authenticated, even if the key name is invalid and the MAC is garbage. As a result, attackers may bypass TSIG authentication on affected transports and access TSIG-protected functionality such as AXFR/IXFR zone transfers, dynamic updates, or other TSIG-gated plugin behavior. ### Details In `server_grpc.go` and `server_quic.go`, the TSIG handling checks whether the TSIG key name exists, but does not call `dns.TsigVerify()`. Relevant code before fix: ```go if tsig := msg.IsTsig(); tsig != nil { if s.tsigSecret == nil { w.tsigStatus = dns.ErrSecret } else if _, ok := s.tsigSecret[tsig.Hdr.Name]; !ok { w.tsigStatus = dns.ErrSecret } // key found -> nothing happens -> tsigStatus stays nil -> "verified" } ``` This means that for gRPC and QUIC, a request with a known TSIG key name but an invalid MAC is accepted as authenticated. PRs #7943 and #7947 partially addressed this area by adding key name checks for gRPC and QUIC, but did not add HMAC verification. The DoH and DoH3 paths have an even weaker failure mode. In `https.go`, `DoHWriter.TsigStatus()` returned nil unconditionally: ```go func (d *DoHWriter) TsigStatus() error { return nil } ``` In `server_https.go`, the incoming DNS message is unpacked from the HTTP request and passed directly into `ServeDNS()` without checking `msg.IsTsig()`, without looking up the TSIG key name, and without calling `dns.TsigVerify()`. The same pattern exists in the DoH3 path in `server_https3.go`. The effective DoH/DoH3 flow before the fix was: 1. HTTP or HTTP/3 request arrives. 2. DNS message is unpacked from the request. 3. A `DoHWriter` is created. 4. The message is passed to `ServeDNS()`. 5. The tsig plugin checks `w.TsigStatus()`. 6. `TsigStatus()` returns nil. 7. nil is interpreted as successful TSIG verification. This means that for DoH and DoH3, CoreDNS did not even require a valid TSIG key name. Any TSIG record was enough to satisfy the tsig plugin, regardless of key name or MAC contents. ### PoC Setup: built CoreDNS from master at commit `12d9457` and also verified against the v1.14.2 release binary. Configured a single test zone with 9 records and `tsig { require all }`. Listeners used the same TSIG configuration and key: - TCP on port 1053, using the normal `dns.Server` path where TSIG HMAC verification works correctly - gRPC on port 1443, using manual TSIG handling - DoH on port 8443 - DoH3 with the same TSIG configuration #### gRPC / QUIC behavior A test client sent AXFR requests over gRPC with a valid TSIG key name but forged MAC values. The same requests were sent over TCP for comparison. | MAC used | gRPC | TCP | |----------|------|-----| | 32 zero bytes | BYPASS, 9 records returned | BADSIG | | 32 random bytes | BYPASS, 9 records returned | BADSIG | | HMAC computed with wrong secret | BYPASS, 9 records returned | BADSIG | | truncated to 16 bytes | BYPASS, 9 records returned | BADSIG | | single byte `0x41` | BYPASS, 9 records returned | BADSIG | | empty MAC | BYPASS, 9 records returned | BADSIG | | wrong key name + zero MAC | REJECTED, NOTAUTH/BADKEY | REJECTED, NOTAUTH/BADKEY | 6 out of 7 forged TSIG requests bypassed authentication over gRPC and returned a full zone transfer. The only rejected case was the wrong key name, because the gRPC path checked whether the key name existed. The same class applied to QUIC. #### DoH / DoH3 behavior For DoH, a test client sent DNS queries over HTTPS POST to `/dns-query` with forged TSIG records. These requests were also compared against TCP. | TSIG variant | DoH result | TCP result | |-------------|------------|------------| | 32 zero bytes | BYPASS, NOERROR | BADSIG | | 32 random bytes | BYPASS, NOERROR | BADSIG | | HMAC computed with wrong secret | BYPASS, NOERROR | BADSIG | | truncated to 16 bytes | BYPASS, NOERROR | BADSIG | | single byte `0x41` | BYPASS, NOERROR | BADSIG | | empty MAC | BYPASS, NOERROR | BADSIG | | bad key name | BYPASS, NOERROR | NOTAUTH/BADKEY | | no TSIG record | REJECTED, REFUSED | REJECTED, REFUSED | 7 out of 8 cases bypassed authentication over DoH. Every request containing a TSIG record was accepted, including requests with an invalid key name. An AXFR request over DoH with a forged TSIG record using a zero-byte MAC returned the full test zone. The same pattern applies to DoH3 because it used the same `DoHWriter` TSIG behavior and did not verify TSIG before passing the message into the plugin chain. To confirm that

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).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

WeaknessesCWE-287

Technical details

References

Community reviews

Related threats