FKIE_CVE-2026-44390

Vulnerability from fkie_nvd - Published: 2026-05-20 10:16 - Updated: 2026-07-29 13:18
Severity
5.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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.
References
sep@nlnetlabs.nlhttps://www.nlnetlabs.nl/downloads/unbound/CVE-2026-44390.txtMitigation, Vendor Advisory
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/errata/RHSA-2026:24013
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/errata/RHSA-2026:36320
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/errata/RHSA-2026:36777
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/errata/RHSA-2026:37282
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/security/cve/CVE-2026-44390
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://bugzilla.redhat.com/show_bug.cgi?id=2480130
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-44390.json
Impacted products
Vendor Product Version
nlnetlabs unbound *
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Unbound",
          "vendor": "NLnet Labs",
          "versions": [
            {
              "lessThan": "1.25.1",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
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      "source": "sep@nlnetlabs.nl"
    },
    {
      "affectedData": [
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          "cpes": [
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          "defaultStatus": "affected",
          "packageName": "unbound",
          "product": "Red Hat Enterprise Linux 10",
          "vendor": "Red Hat",
          "versions": [
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              "status": "unaffected",
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              "versionType": "rpm"
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          "defaultStatus": "affected",
          "packageName": "unbound",
          "product": "Red Hat Enterprise Linux 8",
          "vendor": "Red Hat",
          "versions": [
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              "lessThan": "*",
              "status": "unaffected",
              "version": "0:1.16.2-5.12.el8_10",
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          "packageName": "unbound",
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          "vendor": "Red Hat",
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              "status": "unaffected",
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          "cpes": [
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          "packageName": "rhcos",
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  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
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              "criteria": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "45EC9AEF-23EC-4ECC-A769-18DF07B2CAEC",
              "versionEndExcluding": "1.25.1",
              "vulnerable": true
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          "negate": false,
          "operator": "OR"
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  "cveTags": [],
  "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."
    },
    {
      "lang": "es",
      "value": "NLnet Labs Unbound hasta e incluyendo la versi\u00f3n 1.25.0 tiene una vulnerabilidad al manejar respuestas con RRsets muy grandes para los cuales Unbound necesita realizar compresi\u00f3n de nombres. Respuestas maliciosas de upstream con RRsets muy grandes con registros que no comparten un sufijo por encima de la ra\u00edz pueden causar que Unbound dedique un tiempo considerable a aplicar compresi\u00f3n de nombres a las respuestas de downstream. Esto puede llevar a un rendimiento degradado y eventualmente a una denegaci\u00f3n de servicio en ataques bien orquestados. Un adversario puede explotar la vulnerabilidad consultando a Unbound por el contenido especialmente dise\u00f1ado de una zona maliciosa con RRsets muy grandes. Antes de que Unbound responda a la consulta, intentar\u00e1 aplicar la compresi\u00f3n de nombres, que era una operaci\u00f3n ilimitada que pod\u00eda bloquear la CPU hasta que el paquete completo estuviera listo. Se introdujo un l\u00edmite de compresi\u00f3n en la versi\u00f3n 1.21.1 para esto, pero no tuvo en cuenta el caso en que los registros no compartieran ning\u00fan sufijo por encima de la ra\u00edz. Eso hace que Unbound siga una ruta de c\u00f3digo diferente debido al fallo en la b\u00fasqueda del \u00e1rbol de compresi\u00f3n y, finalmente, no incremente el contador de compresi\u00f3n para esas operaciones. Unbound 1.25.1 contiene un parche con una correcci\u00f3n que incrementa el contador de compresi\u00f3n independientemente de la b\u00fasqueda del \u00e1rbol de compresi\u00f3n. Esta es una correcci\u00f3n complementaria para CVE-2024-8508."
    }
  ],
  "id": "CVE-2026-44390",
  "lastModified": "2026-07-29T13:18:38.747",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "LOW",
          "baseScore": 5.3,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
          "version": "3.1"
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        "source": "nvd@nist.gov",
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          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
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    "cvssMetricV40": [
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          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
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          "baseSeverity": "MEDIUM",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "AMBER",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber",
          "version": "4.0",
          "vulnAvailabilityImpact": "LOW",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "sep@nlnetlabs.nl",
        "type": "Secondary"
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    "ssvcV203": [
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        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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          "options": [
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            {
              "automatable": "yes"
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            {
              "technicalImpact": "partial"
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          "role": "CISA Coordinator",
          "timestamp": "2026-05-20T12:55:48.767374Z",
          "version": "2.0.3"
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  "published": "2026-05-20T10:16:28.183",
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      "tags": [
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  "vulnStatus": "Modified",
  "weaknesses": [
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          "value": "CWE-407"
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      "type": "Secondary"
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          "value": "CWE-1050"
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}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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