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

What is affected, what to do

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.

Update NLnet Labs Unbound to version 1.25.2.

Affected

• NLnet Labs Unbound lt 1.15.0..1.25.2

Fixed in

• NLnet Labs Unbound 1.25.2

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2

NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

Read in glossary

Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.

CRA

The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

Read in glossary

From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.

ISO/IEC 27001

ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

Read in glossary

Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

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.

Source: Debian Security Advisories, BSI CSAF, BSI WID Portal, redhat_csaf, suse_csaf, NVD (NIST), Microsoft Security Update Guide, cvelistv5

Vendors and products

• Debian Unbound
• Meinberg Lantime
• Nlnet Labs Unbound
• NLnet Labs NLnet Labs Unbound
• Open Source Unbound

Weakness classes (CWE)

• CWE-416Use After Free

  Variant

  The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

  Entry at MITRE CWE-416

References & sources

• nlnetlabs.nldownloads/unbound/CVE-2026-50046.txtVendor advisory, Vendor advisory

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

1. 24.07.2026Initial analysis by NVDNVD

   Newly listed as affected:

   • NLnet Labs Unbound (1.15.0 – before 1.25.2)

   New references:

   • https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50046.txt
   Show 2 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Product configuration	added	—	OR *cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:* versions from (including) 1.15.0 up to (excluding) 1.25.2
   Reference type	added	—	NLnet Labs: https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50046.txt Types: Vendor Advisory

   Source identifier: nvd@nist.gov

2. 22.07.2026Record modifiedCISA ADP

   CISA assessment (SSVC): exploitation: none known, automatable: no

   Show the original change

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   SSVC assessment	added	—	{"id":"CVE-2026-50046","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-07-22T18:57:24.481710Z"}

   Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

3. 22.07.2026Receivednlnetlabs.nl

   CVSS V3.1: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

   Weakness type: CWE-416

   Description added or changed

   New references:

   • https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50046.txt
   Show 5 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Affected versions (publisher)	added	—	Unbound
   Description	added	—	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.
   CVSS	added	—	AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
   Weakness type (CWE)	added	—	CWE-416
   Reference	added	—	https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50046.txt

   Source identifier: sep@nlnetlabs.nl

One NVD translation into another language is hidden.