Vulnerability-Lookup

ubuntu-cve-2026-55717

Vulnerability from osv_ubuntu

Published

2026-07-22 14:17

Modified

2026-07-29 07:59

Summary

Details

In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: redirect' /'response-ip-data: CNAME ' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets 'alias_rrset' but not 'partial_rep'. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of 'serve-expired-client-timeout' is taken leading to denial of service via the server crash.

Severity

5.9 (Medium)


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

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-55717	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-55717	REPORT
	https://community.nlnetlabs.nl/t/unbound-1-25-2-r…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "libunbound2",
            "binary_version": "1.4.22-1ubuntu4.14.04.3+esm3"
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      },
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        "1.4.22-1ubuntu4",
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    },
    {
      "ecosystem_specific": {
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            "binary_name": "python3-unbound",
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            "binary_name": "unbound",
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          },
          {
            "binary_name": "unbound-anchor",
            "binary_version": "1.13.1-1ubuntu5.15"
          },
          {
            "binary_name": "unbound-host",
            "binary_version": "1.13.1-1ubuntu5.15"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:22.04:LTS",
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      },
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        }
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        "1.13.1-1ubuntu3",
        "1.13.1-1ubuntu5",
        "1.13.1-1ubuntu5.1",
        "1.13.1-1ubuntu5.2",
        "1.13.1-1ubuntu5.3",
        "1.13.1-1ubuntu5.4",
        "1.13.1-1ubuntu5.5",
        "1.13.1-1ubuntu5.7",
        "1.13.1-1ubuntu5.8",
        "1.13.1-1ubuntu5.10",
        "1.13.1-1ubuntu5.11",
        "1.13.1-1ubuntu5.12",
        "1.13.1-1ubuntu5.13",
        "1.13.1-1ubuntu5.14",
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          {
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            "binary_version": "1.24.2-1ubuntu2.1"
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            "binary_version": "1.24.2-1ubuntu2.1"
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          {
            "binary_name": "unbound-anchor",
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        "1.24.2-1ubuntu2",
        "1.24.2-1ubuntu2.1"
      ]
    }
  ],
  "aliases": [],
  "details": "In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when \u0027serve-expired: yes\u0027 is set together with a \u0027response-ip: \u003cnet\u003e redirect\u0027 /\u0027response-ip-data: \u003cnet\u003e CNAME \u003ctarget\u003e\u0027 rule (or the RPZ \u0027rpz-cname-override\u0027 equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets \u0027alias_rrset\u0027 but not \u0027partial_rep\u0027. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of \u0027serve-expired-client-timeout\u0027 is taken leading to denial of service via the server crash.",
  "id": "UBUNTU-CVE-2026-55717",
  "modified": "2026-07-29T07:59:15Z",
  "published": "2026-07-22T14:17:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-55717"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-55717"
    },
    {
      "type": "REPORT",
      "url": "https://community.nlnetlabs.nl/t/unbound-1-25-2-released/3430"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-55717"
  ]
}

CVE-2026-55717 (GCVE-0-2026-55717)

Vulnerability from cvelistv5 – Published: 2026-07-22 13:09 – Updated: 2026-07-22 14:07

Title

'serve-expired-client-timeout' and 'response-ip' CNAME redirect could lead to a crash

Summary

In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: <net> redirect' /'response-ip-data: <net> CNAME <target>' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets 'alias_rrset' but not 'partial_rep'. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of 'serve-expired-client-timeout' is taken leading to denial of service via the server crash.

Severity

5.9 (Medium)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-07-22 14:07 UTC

CWE

CWE-476 - NULL Pointer Dereference

Assigner

NLnet Labs

References

1 reference

URL	Tags
https://www.nlnetlabs.nl/downloads/unbound/CVE-20…	vendor-advisory

Impacted products

1 product

Vendor	Product	Version
NLnet Labs	Unbound	Affected: 1.10.0 , < 1.25.2 (semver)

Date Public

2026-07-22 00:00

Credits

Qifan Zhang (Palo Alto Networks) Xin Wang (Northwestern Polytechnical University) Jiapeng Li (Northwestern Polytechnical University) Jiajia Liu (Northwestern Polytechnical University)

Show details on NVD website

JSON

To clipboard

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    "datePublished": "2026-07-22T13:09:40.927Z",
    "dateReserved": "2026-06-22T12:27:22.813Z",
    "dateUpdated": "2026-07-22T14:07:31.075Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

ubuntu-cve-2026-55717

Vulnerability from osv_ubuntu

CVE-2026-55717 (GCVE-0-2026-55717)

Tags

Sightings

Nomenclature