CVE-2026-77639 (GCVE-0-2026-77639)

Vulnerability from cvelistv5 – Published: 2026-08-20 20:57 – Updated: 2026-08-20 20:57
VLAI
Summary
Tor before 0.4.9.9 was prone to a compression bomb bypass where an attacker could concatenate many gzip or zlib sub-streams, each just under the per-stream detection threshold, to avoid the compression bomb check entirely. This is TROVE-2026-022.
CWE
  • CWE-420 - Unprotected Alternate Channel
Impacted products
Vendor Product Version CPE status
torproject Tor Affected: 0.3.1.1-alpha , < 0.4.9.9 (custom)
    cpe:2.3:a:torproject:tor:*:*:*:*:*:*:*:*
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Show details on NVD website

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Tor",
          "vendor": "torproject",
          "versions": [
            {
              "lessThan": "0.4.9.9",
              "status": "affected",
              "version": "0.3.1.1-alpha",
              "versionType": "custom"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:a:torproject:tor:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "0.4.9.9",
                  "versionStartIncluding": "0.3.1.1-alpha",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Tor before 0.4.9.9 was prone to a\u00a0compression bomb bypass where an attacker could concatenate many gzip or zlib sub-streams, each just under the per-stream detection threshold, to avoid the compression bomb check entirely. This is TROVE-2026-022."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "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"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-420",
              "description": "CWE-420 Unprotected Alternate Channel",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-20T20:57:50.207Z",
        "orgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca",
        "shortName": "mitre"
      },
      "references": [
        {
          "url": "https://gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.9.9/ChangeLog"
        }
      ],
      "x_generator": {
        "engine": "CVE-Request-form 0.0.1"
      }
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  },
  "cveMetadata": {
    "assignerOrgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca",
    "assignerShortName": "mitre",
    "cveId": "CVE-2026-77639",
    "datePublished": "2026-08-20T20:57:50.207Z",
    "dateReserved": "2026-08-20T20:57:49.855Z",
    "dateUpdated": "2026-08-20T20:57:50.207Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-77639\",\"sourceIdentifier\":\"cve@mitre.org\",\"published\":\"2026-08-20T21:17:11.233\",\"lastModified\":\"2026-08-20T21:17:11.233\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Tor before 0.4.9.9 was prone to a\u00a0compression bomb bypass where an attacker could concatenate many gzip or zlib sub-streams, each just under the per-stream detection threshold, to avoid the compression bomb check entirely. This is TROVE-2026-022.\"}],\"affected\":[{\"source\":\"cve@mitre.org\",\"affectedData\":[{\"vendor\":\"torproject\",\"product\":\"Tor\",\"defaultStatus\":\"unaffected\",\"versions\":[{\"version\":\"0.3.1.1-alpha\",\"lessThan\":\"0.4.9.9\",\"versionType\":\"custom\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"cve@mitre.org\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L\",\"baseScore\":5.3,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"LOW\"},\"exploitabilityScore\":3.9,\"impactScore\":1.4}]},\"weaknesses\":[{\"source\":\"cve@mitre.org\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-420\"}]}],\"references\":[{\"url\":\"https://gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.9.9/ChangeLog\",\"source\":\"cve@mitre.org\"}]}}"
  }
}



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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.

Sightings

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Nomenclature

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