NVD / CVE Program· CNA NLnet Labs

CVE-2026-50046: Possible heap use-after-free in an error path when a DoT forwarded query is jostled out

Noroxi assessment

Priority: Monitor (action score 23/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.23% (FIRST EPSS).
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.
Fixed version: NLnet Labs Unbound 1.25.2; azl3 unbound 1.25.1-1 on Azure Linux 3.0 1.25.2-1.

Low priority for now. Upgrade to NLnet Labs Unbound 1.25.2; azl3 unbound 1.25.1-1 on Azure Linux 3.0 1.25.2-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In NLnet Labs Unbound 1.15.0 up to and including 1.25.1, the TLS server name used for DNS-over-TLS (DoT) forwarded queries is tied to a struct's ('serviced_query') lifetime but also referenced by another struct ('waiting_tcp'). When the owning struct is jostled out of the mesh while the DoT TCP stream is still handshaking it frees the storage behind the referenced string and if the TLS stream then errors out, it dereferences the freed pointer. The dereference is read-only and the practical impact is a daemon crash resulting in denial of service. A malicious actor that knows a DoT forwarding/stub Unbound's configuration could exploit the vulnerability by quering records in the appropriate zone while keeping Unbound uder pressure so that the jostle logic kicks in. If answers for the vulnerable zone are slow, the likelihood of jostling such queries is higher, although the timing of the jostle needs to be precise. Requirements for a vulnerable Unbound is the existence of a stub/forward zone configured for DoT together with a configured '#authname' suffix on the server identification. The connectivity to the server needs to exhibit a transient failure at the correct time in order to kick off the vulnerable error path.

MediumCVSS 5.9 · v3.1—No exploit Fix available

Published: Jul 22, 2026
Updated: Oct 24, 2026
EPSS: 0.2% · 14th percentile
CWE: CWE-416

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 23 / 40 · 5.9 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · NLnet Labs: 5.9; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
nlnetlabs	unbound	cpe:2.3:a:nlnetlabs:unbound

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

nlnetlabs unbound1.15.0 and later · before 1.25.2

Versions reported by the vendor

Affected version ranges reported by the assigning authority (NLnet Labs). Independent of NVD's CPE analysis and usually ahead of it.

NLnet Labs Unbound
- 1.15.0 and later · before 1.25.2affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Alpine:v3.22	unbound	from 1.15.0 · before 1.25.2-r0	1.25.2-r0
Debian:12	unbound	from 0	—
Debian:13	unbound	before 1.26.1-0+deb13u1	1.26.1-0+deb13u1
Debian:14	unbound	before 1.25.2-1	1.25.2-1
openSUSE:Leap 16.0	unbound	before 1.25.2-160000.1.1	1.25.2-160000.1.1
openSUSE:Tumbleweed	unbound	before 1.25.2-1.1	1.25.2-1.1
Red Hat:hummingbird:1	python3-unbound	before 0:1.25.2-0.1.hum1	0:1.25.2-0.1.hum1
Red Hat:hummingbird:1	unbound	before 0:1.25.2-0.1.hum1	0:1.25.2-0.1.hum1
Red Hat:hummingbird:1	unbound-anchor	before 0:1.25.2-0.1.hum1	0:1.25.2-0.1.hum1
Red Hat:hummingbird:1	unbound-devel	before 0:1.25.2-0.1.hum1	0:1.25.2-0.1.hum1
Red Hat:hummingbird:1	unbound-dracut	before 0:1.25.2-0.1.hum1	0:1.25.2-0.1.hum1
Red Hat:hummingbird:1	unbound-libs	before 0:1.25.2-0.1.hum1	0:1.25.2-0.1.hum1
Red Hat:hummingbird:1	unbound-munin	before 0:1.25.2-0.1.hum1	0:1.25.2-0.1.hum1
Red Hat:hummingbird:1	unbound-utils	before 0:1.25.2-0.1.hum1	0:1.25.2-0.1.hum1
SUSE:Linux Enterprise Micro 5.5	unbound	before 1.25.2-150100.10.28.1	1.25.2-150100.10.28.1
SUSE:Linux Enterprise Module for Basesystem 15 SP7	unbound	before 1.25.2-150600.23.19.1	1.25.2-150600.23.19.1
SUSE:Linux Micro 6.0	unbound	before 1.25.2-1.1	1.25.2-1.1
SUSE:Linux Micro 6.1	unbound	before 1.25.2-slfo.1.1_1.1	1.25.2-slfo.1.1_1.1
SUSE:Linux Micro 6.2	unbound	before 1.25.2-160000.1.1	1.25.2-160000.1.1

Same product

nlnetlabs: all records

Other highest-scoring records for the same primary product.

CVE-2019-25042Unbound before 1.9.5 allows an out-of-bounds write via a compressed name in rdata_copy.
40Plan
CVE-2019-25039Unbound before 1.9.5 allows an integer overflow in a size calculation in respip/respip.c.
40Plan
CVE-2019-25038Unbound before 1.9.5 allows an integer overflow in a size calculation in dnscrypt/dnscrypt.c.
40Plan

Published before and after this one in the same product

← EarlierCVE-2026-46582Jul 22, 2026 · A wildcard replay, as another piece of data, triggers poisoning in the serve expired reply path
14Monitor
← EarlierCVE-2026-50045Jul 22, 2026 · 'max-global-quota' reset by DNSSEC validation restarts
21Monitor
Later →CVE-2026-50243Jul 22, 2026 · 'response-ip'/'rpz' can rewrite BOGUS answers instead of returning SERVFAIL
25Monitor

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
NLnet Labs Unbound	1.25.2	Vendor (CNA)
azl3 unbound 1.25.1-1 on Azure Linux 3.0	1.25.2-1 · CBL-Mariner Releases	Microsoft (MSRC)
alpine:unbound	1.25.2-r0 · Alpine:v3.22	Package registry (OSV)
debian:unbound	1.26.1-0+deb13u1 · Debian:13	Package registry (OSV)
opensuse:unbound	1.25.2-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
red hat:python3-unbound	0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
red hat:unbound	0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
red hat:unbound-anchor	0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
red hat:unbound-devel	0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
red hat:unbound-dracut	0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
red hat:unbound-libs	0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
red hat:unbound-munin	0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
red hat:unbound-utils	0:1.25.2-0.1.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
suse:unbound	1.25.2-160000.1.1 · SUSE:Linux Micro 6.2	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.

EPSS, last 120 days

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 researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Qifan Zhang (Palo Alto Networks)finder

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-3327863 days apartPossible arbitrary code execution during DNSSEC validation
36Monitor
CVE-2026-7822756 days apartUse-after-free in DoQ stream output buffer on reset re-transmission
26Monitor
CVE-2026-528630 days apartMemory corruption could lead to crash and denial of service
23Monitor
CVE-2026-8272056 days apartUse-after-free in DoH stream cleanup code path
23Monitor

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-416 · Use After Free

CVSS vector

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

nvd-secondary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

Fix✗ → ✓Sep 28, 2026, 10:10 PM UTC

For records you follow, these changes also arrive as notifications. →

References

www.nlnetlabs.nl/downloads/unbound/CVE-2026-50046.txt

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records