GHSA-2wpx-qpw2-g5h5 CVE-2026-32934 GO-2026-4969
CoreDNS' DoQ worker pool does not bound stream backlog
- Severity
- 0.0 / 10
- High · CVSS 4.0
- Exploit chance (EPSS)
- 0.47%
- Chance of exploitation in the next 30 days. Higher than 40.58% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-770 Allocation of Resources Without Limits or Throttling
- Fix
1.14.3- Upgrade github.com/coredns/coredns to this version or later
Description
Summary
CoreDNS' DNS-over-QUIC (DoQ) server can be driven into large goroutine and memory growth by a remote client that opens many QUIC streams and stalls after sending only 1 byte. Even with a small configured quic { worker_pool_size ... }, CoreDNS still spawns a goroutine per accepted stream (workers + waiters) and active workers can block indefinitely in io.ReadFull() with no per-stream read deadline, enabling unauthenticated remote DoS via memory exhaustion/OOM-kill.
Details
CoreDNS' DoQ server uses a global worker pool (streamProcessPool) to limit concurrent stream processing, but when the pool is full it still spawns a goroutine per accepted stream that waits to acquire a worker token: select { case s.streamProcessPool <- ...: go ...; default: go ... wait for token ... } (core/dnsserver/server_quic.go)
Additionally, the DoQ message framing reads are blocking io.ReadFull() calls with no per-stream read deadline: readDOQMessage() reads the 2-byte length prefix and message body via io.ReadFull() (core/dnsserver/server_quic.go)
This allows an attacker to pin all workers by sending 1 byte (so io.ReadFull() blocks waiting for the second byte of the DoQ length prefix), while also creating an unbounded backlog of goroutines waiting for a worker token.
Note: this appears to be a result of an incomplete fix/regression for CVE-2025-47950 (GHSA-cvx7-x8pj-x2gw).
PoC
- Adjust COREDNS_BIN in the PoC to point at right path (see the top-level const definitions for tunables as well)
- Run python3 ./doq-dos-repro.py
- Expected sample output: *** Start CoreDNS *** Corefile: /tmp/vh-f003-doq-mem-regression/Corefile Log: /tmp/vh-f003-doq-mem-regression/coredns.log
*** Baseline sample (idle) *** rss_kib=49380 go_goroutines=17
*** Build + run partial-stream flooder *** go: downloading golang.org/x/net v0.43.0 go: downloading golang.org/x/crypto v0.41.0 go: downloading go.uber.org/mock v0.5.2 go: downloading github.com/stretchr/testify v1.11.1 go: downloading golang.org/x/sys v0.35.0 go: downloading github.com/pmezard/go-difflib v1.0.0 go: downloading github.com/davecgh/go-spew v1.1.1 go: downloading gopkg.in/yaml.v3 v3.0.1
*** Candidate sample (during attack) *** rss_kib=137968 go_goroutines=15557
*** Flooder output *** opened conns=60 streams_per_conn=256 total_streams=15360
*** Wrote results *** /tmp/vh-f003-doq-mem-regression/results.json
*** OK *** DoQ flood caused goroutine/RSS growth despite worker_pool_size.
Impact
Unauthenticated remote DoS on an encrypted DNS transport via goroutine/RSS growth leading to OOM-kill/crash and service outage.
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| github.com/coredns/coredns | < 1.14.3 |
1.14.3 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
github.com/coredns/coredns Go → 1.14.3
- go
go get github.com/coredns/coredns@v1.14.3 && go mod tidy
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- High
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Weakness
CWE-770: Allocation of Resources Without Limits or Throttling
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
How to prevent it
- Requirements: Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
- Architecture and Design: Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
- Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place, and it will help the administrator to identify who is committing the abuse. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
- Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, typically by using increasing time delays uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution can be difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply requires more resources on the part of the attacker.
- Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
- Architecture and Design, Implementation: If the program must fail, ensure that it fails gracefully (fails closed). There may be a temptation to simply let the program fail poorly in cases such as low memory conditions, but an attacker may be able to assert control before the software has fully exited. Alternately, an uncontrolled failure could cause cascading problems with other downstream components; for example, the program could send a signal to a downstream process so the process immediately knows that a problem has occurred and has a better chance of recovery. Ensure that all failures in resource allocation place the system into a safe posture.
- Operation, Architecture and Design: Use quotas or other resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-9gm5-9rfh-m6vx CoreDNS DoH/DoQ/gRPC bypass UPDATE rejection enforced on UDP/TCP | High | Also affects github.com/coredns/coredns |
| GHSA-mrg3-qvqr-jw29 CoreDNS: Unauthenticated memory exhaustion in custom transports | High | Also affects github.com/coredns/coredns |
| GHSA-74w3-63xv-x9mv CoreDNS `k8s_external` headless AXFR can emit an empty transfer batch that panics the `transfer` plugin | Low | Also affects github.com/coredns/coredns |
| GHSA-vp29-5652-4fw9 CoreDNS has TSIG authentication bypass on gRPC and QUIC transports | Critical | Also affects github.com/coredns/coredns |
| GHSA-qhmp-q7xh-99rh CoreDNS has TSIG authentication bypass on DoT, DoH, DoH3, DoQ, and gRPC | High | Also affects github.com/coredns/coredns |
| GHSA-h8mm-c463-wjq3 CoreDNS' transfer stanza selection uses lexicographic compare (subzone ACL bypass) | High | Also affects github.com/coredns/coredns |
| GHSA-63cw-r7xf-jmwr CoreDNS DoH GET oversized dns= query parameter causes pre-validation CPU and memory amplification | High | Also affects github.com/coredns/coredns |
| GHSA-h75p-j8xm-m278 CoreDNS Loop Detection Denial of Service Vulnerability | High | Also affects github.com/coredns/coredns |
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