CVE-2026-44390 (GCVE-0-2026-44390)

Vulnerability from cvelistv5 – Published: 2026-05-20 09:21 – Updated: 2026-09-01 12:04
VLAI
Title
Unbounded name compression in certain cases causes degradation of service
Summary
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability when handling replies with very large RRsets that Unbound needs to perform name compression for. Malicious upstream responses with very large RRsets with records that don't share a suffix above the root can cause Unbound to spend a considerable time applying name compression to downstream replies. This can lead to degraded performance and eventually denial of service in well orchestrated attacks. An adversary can exploit the vulnerability by querying Unbound for the specially crafted contents of a malicious zone with very large RRsets. Before Unbound replies to the query it will try to apply name compression which was an unbounded operation that could lock the CPU until the whole packet was complete. A compression limit was introduced in 1.21.1 for this but it didn't account for the case where records would not share any suffix above the root. That causes Unbound to go in a different code path because of the compression tree lookup failure and eventually not increment the compression counter for those operations. Unbound 1.25.1 contains a patch with a fix that increments the compression counter regardless of the compression tree lookup. This is a complement fix to CVE-2024-8508.
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-05-20 12:55 UTC
CWE
  • CWE-407 - Inefficient Algorithmic Complexity
  • CWE-1050 - Excessive Platform Resource Consumption within a Loop
Assigner
References
Impacted products
Vendor Product Version
NLnet Labs Unbound Affected: 0 , < 1.25.1 (semver)
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Red Hat Red Hat Enterprise Linux 10 Unaffected: 0:1.24.2-7.el10_2.2 , < * (rpm)
    cpe:/o:redhat:enterprise_linux:10.2
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Red Hat Red Hat Enterprise Linux 8 Unaffected: 0:1.16.2-5.12.el8_10 , < * (rpm)
    cpe:/a:redhat:enterprise_linux:8
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Red Hat Red Hat Enterprise Linux 9 Unaffected: 0:1.24.2-3.el9_8.2 , < * (rpm)
    cpe:/a:redhat:enterprise_linux:9
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Red Hat Red Hat Hardened Images Unaffected: 1.25.1-2.hum1 , < * (rpm)
    cpe:/a:redhat:hummingbird:1
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Red Hat Red Hat Enterprise Linux 6     cpe:/o:redhat:enterprise_linux:6
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Red Hat Red Hat Enterprise Linux 7     cpe:/o:redhat:enterprise_linux:7
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Red Hat Red Hat OpenShift Container Platform 4     cpe:/a:redhat:openshift:4
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Date Public
2026-05-20 00:00
Show details on NVD website

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                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-05-20T12:56:24.222Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "defaultStatus": "unaffected",
              "product": "Unbound",
              "vendor": "NLnet Labs",
              "versions": [
                {
                  "lessThan": "1.25.1",
                  "status": "affected",
                  "version": "0",
                  "versionType": "semver"
                }
              ]
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "finder",
              "value": "Qifan Zhang (Palo Alto Networks)"
            }
          ],
          "datePublic": "2026-05-20T00:00:00.000Z",
          "descriptions": [
            {
              "lang": "en",
              "value": "NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability when handling replies with very large RRsets that Unbound needs to perform name compression for. Malicious upstream responses with very large RRsets with records that don\u0027t share a suffix above the root can cause Unbound to spend a considerable time applying name compression to downstream replies. This can lead to degraded performance and eventually denial of service in well orchestrated attacks. An adversary can exploit the vulnerability by querying Unbound for the specially crafted contents of a malicious zone with very large RRsets. Before Unbound replies to the query it will try to apply name compression which was an unbounded operation that could lock the CPU until the whole packet was complete. A compression limit was introduced in 1.21.1 for this but it didn\u0027t account for the case where records would not share any suffix above the root. That causes Unbound to go in a different code path because of the compression tree lookup failure and eventually not increment the compression counter for those operations. Unbound 1.25.1 contains a patch with a fix that increments the compression counter regardless of the compression tree lookup. This is a complement fix to CVE-2024-8508."
            }
          ],
          "metrics": [
            {
              "cvssV4_0": {
                "baseScore": 6.9,
                "baseSeverity": "MEDIUM",
                "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/U:Amber",
                "version": "4.0"
              },
              "format": "CVSS",
              "scenarios": [
                {
                  "lang": "en",
                  "value": "GENERAL"
                }
              ]
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-407",
                  "description": "CWE-407: Inefficient Algorithmic Complexity",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-05-20T09:21:24.590Z",
            "orgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
            "shortName": "NLnet Labs"
          },
          "references": [
            {
              "tags": [
                "vendor-advisory"
              ],
              "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-44390.txt"
            }
          ],
          "solutions": [
            {
              "lang": "en",
              "value": "This issue is fixed starting with version 1.25.1"
            }
          ],
          "timeline": [
            {
              "lang": "en",
              "time": "2026-04-26T00:00:00.000Z",
              "value": "Issue reported by Qifan Zhang"
            },
            {
              "lang": "en",
              "time": "2026-04-28T00:00:00.000Z",
              "value": "NLnet Labs shares patch"
            },
            {
              "lang": "en",
              "time": "2026-04-29T00:00:00.000Z",
              "value": "Qifan Zhang verifies patch"
            },
            {
              "lang": "en",
              "time": "2026-05-20T00:00:00.000Z",
              "value": "Fixes released with version 1.25.1"
            }
          ],
          "title": "Unbounded name compression in certain cases causes degradation of service",
          "x_generator": {
            "engine": "cvelib 1.8.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
        "assignerShortName": "NLnet Labs",
        "cveId": "CVE-2026-44390",
        "datePublished": "2026-05-20T09:21:24.590Z",
        "dateReserved": "2026-05-07T10:07:51.828Z",
        "dateUpdated": "2026-09-01T12:04:42.716Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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