CVE-2026-63896 (GCVE-0-2026-63896)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-07-19 14:55
VLAI
Title
usb: gadget: composite: fix integer underflow in WebUSB GET_URL handling
Summary
In the Linux kernel, the following vulnerability has been resolved: usb: gadget: composite: fix integer underflow in WebUSB GET_URL handling The WebUSB GET_URL handler in composite_setup() narrows landing_page_length to fit the host-supplied wLength using landing_page_length = w_length - WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + landing_page_offset; If wLength is smaller than WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH the unsigned subtraction wraps, and the subsequent memcpy(url_descriptor->URL, cdev->landing_page + landing_page_offset, landing_page_length - landing_page_offset); ends up copying close to UINT_MAX bytes from cdev->landing_page into cdev->req->buf. KASAN reports a slab-out-of-bounds in composite_setup on the kmalloc-2k gadget_info allocation, and FORTIFY_SOURCE traps the memcpy as a 4294967293-byte field-spanning write into url_descriptor->URL (size 252). A USB host can reach this from a single SETUP packet against any gadget that has webusb/use=1 and a landingPage configured. Handle the small-wLength case before the math: when the host requested fewer bytes than the URL descriptor header, only the header is meaningful and no URL bytes need to be copied. Setting landing_page_length to landing_page_offset makes the existing memcpy a no-op and leaves the descriptor returned to the host unchanged for all larger wLength values.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 93c473948c588978cd55d9a3adad8b3e8057aa21 , < 046870ff6b6f7b743c953c061043a9b30700d491 (git)
Affected: 93c473948c588978cd55d9a3adad8b3e8057aa21 , < f5869dfaa89854dcf34121036294d42d6c7acb8f (git)
Affected: 93c473948c588978cd55d9a3adad8b3e8057aa21 , < f8f5a8f48c7cae3fac85e04b593bd47939f9725f (git)
Affected: 93c473948c588978cd55d9a3adad8b3e8057aa21 , < a20f0ccf45708af6e063c7234c215d364b00de25 (git)
Affected: 93c473948c588978cd55d9a3adad8b3e8057aa21 , < 6c5dbc104dadd79fc2923497c20bae759a18758c (git)
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Linux Linux Affected: 6.3
Unaffected: 0 , < 6.3 (semver)
Unaffected: 6.6.143 , ≤ 6.6.* (semver)
Unaffected: 6.12.93 , ≤ 6.12.* (semver)
Unaffected: 6.18.35 , ≤ 6.18.* (semver)
Unaffected: 7.0.12 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
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{
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/usb/gadget/composite.c"
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          "vendor": "Linux",
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      "cpeApplicability": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: composite: fix integer underflow in WebUSB GET_URL handling\n\nThe WebUSB GET_URL handler in composite_setup() narrows\nlanding_page_length to fit the host-supplied wLength using\n\n\tlanding_page_length = w_length\n\t\t- WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + landing_page_offset;\n\nIf wLength is smaller than WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH the\nunsigned subtraction wraps, and the subsequent\n\n\tmemcpy(url_descriptor-\u003eURL,\n\t       cdev-\u003elanding_page + landing_page_offset,\n\t       landing_page_length - landing_page_offset);\n\nends up copying close to UINT_MAX bytes from cdev-\u003elanding_page into\ncdev-\u003ereq-\u003ebuf.  KASAN reports a slab-out-of-bounds in composite_setup\non the kmalloc-2k gadget_info allocation, and FORTIFY_SOURCE traps the\nmemcpy as a 4294967293-byte field-spanning write into\nurl_descriptor-\u003eURL (size 252).\n\nA USB host can reach this from a single SETUP packet against any\ngadget that has webusb/use=1 and a landingPage configured.\n\nHandle the small-wLength case before the math: when the host requested\nfewer bytes than the URL descriptor header, only the header is\nmeaningful and no URL bytes need to be copied.  Setting\nlanding_page_length to landing_page_offset makes the existing memcpy a\nno-op and leaves the descriptor returned to the host unchanged for all\nlarger wLength values."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-19T14:55:06.152Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/046870ff6b6f7b743c953c061043a9b30700d491"
        },
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          "url": "https://git.kernel.org/stable/c/f5869dfaa89854dcf34121036294d42d6c7acb8f"
        },
        {
          "url": "https://git.kernel.org/stable/c/f8f5a8f48c7cae3fac85e04b593bd47939f9725f"
        },
        {
          "url": "https://git.kernel.org/stable/c/a20f0ccf45708af6e063c7234c215d364b00de25"
        },
        {
          "url": "https://git.kernel.org/stable/c/6c5dbc104dadd79fc2923497c20bae759a18758c"
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      "title": "usb: gadget: composite: fix integer underflow in WebUSB GET_URL handling",
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    "cveId": "CVE-2026-63896",
    "datePublished": "2026-07-19T14:55:06.152Z",
    "dateReserved": "2026-07-19T07:54:57.019Z",
    "dateUpdated": "2026-07-19T14:55:06.152Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
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      "date": "2026-07-21",
      "epss": "0.002",
      "percentile": "0.10012"
    },
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-07-21T11:11:20+00:00",
      "cve": "CVE-2026-63896",
      "id": "CVE-2026-63896",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_affected": "76",
      "product_status:known_not_affected": "198",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: usb: gadget: composite: fix integer underflow in WebUSB GET_URL handling",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63896.json",
      "version": "3"
    }
  }
}



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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

  • 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.


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