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CVE-2025-39967 (GCVE-0-2025-39967)

Vulnerability from cvelistv5 – Published: 2025-10-15 07:55 – Updated: 2026-08-05 12:06
VLAI
Title
fbcon: fix integer overflow in fbcon_do_set_font
Summary
In the Linux kernel, the following vulnerability has been resolved: fbcon: fix integer overflow in fbcon_do_set_font Fix integer overflow vulnerabilities in fbcon_do_set_font() where font size calculations could overflow when handling user-controlled font parameters. The vulnerabilities occur when: 1. CALC_FONTSZ(h, pitch, charcount) performs h * pith * charcount multiplication with user-controlled values that can overflow. 2. FONT_EXTRA_WORDS * sizeof(int) + size addition can also overflow 3. This results in smaller allocations than expected, leading to buffer overflows during font data copying. Add explicit overflow checking using check_mul_overflow() and check_add_overflow() kernel helpers to safety validate all size calculations before allocation.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-06-10 20:42 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 96e41fc29e8af5c5085fb8a79cab8d0d00bab86c , < 994bdc2d23c79087fbf7dcd9544454e8ebcef877 (git)
Affected: 39b3cffb8cf3111738ea993e2757ab382253d86a , < 9c8ec14075c5317edd6b242f1be8167aa1e4e333 (git)
Affected: 39b3cffb8cf3111738ea993e2757ab382253d86a , < b8a6e85328aeb9881531dbe89bcd2637a06c3c95 (git)
Affected: 39b3cffb8cf3111738ea993e2757ab382253d86a , < a6eb9f423b3db000aaedf83367b8539f6b72dcfc (git)
Affected: 39b3cffb8cf3111738ea993e2757ab382253d86a , < adac90bb1aaf45ca66f9db8ac100be16750ace78 (git)
Affected: 39b3cffb8cf3111738ea993e2757ab382253d86a , < 4a4bac869560f943edbe3c2b032062f6673b13d3 (git)
Affected: 39b3cffb8cf3111738ea993e2757ab382253d86a , < c0c01f9aa08c8e10e10e8c9ebb5be01a4eff6eb7 (git)
Affected: 39b3cffb8cf3111738ea993e2757ab382253d86a , < 1a194e6c8e1ee745e914b0b7f50fa86c89ed13fe (git)
Affected: ae021a904ac82d9fc81c25329d3c465c5a7d5686 (git)
Affected: 451bffa366f2cc0e5314807cb847f31c0226efed (git)
Affected: 2c455e9c5865861f5ce09c5f596909495ed7657c (git)
Affected: 72f099805dbc907fbe8fa19bccdc31d3e2ee6e9e (git)
Affected: 34cf1aff169dc6dedad8d79da7bf1b4de2773dbc (git)
Affected: 5.4.62 , < 5.4.300 (semver)
Affected: 4.4.235 , < 4.5 (semver)
Affected: 4.9.235 , < 4.10 (semver)
Affected: 4.14.196 , < 4.15 (semver)
Affected: 4.19.143 , < 4.20 (semver)
Affected: 5.8.6 , < 5.9 (semver)
guessed Create a notification for this product.
Linux Linux Affected: 5.9
Unaffected: 0 , < 5.9 (semver)
Unaffected: 5.4.300 , ≤ 5.4.* (semver)
Unaffected: 5.10.245 , ≤ 5.10.* (semver)
Unaffected: 5.15.194 , ≤ 5.15.* (semver)
Unaffected: 6.1.155 , ≤ 6.1.* (semver)
Unaffected: 6.6.109 , ≤ 6.6.* (semver)
Unaffected: 6.12.50 , ≤ 6.12.* (semver)
Unaffected: 6.16.10 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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              "value": "AV:L - The only route to `fbcon_set_font()` is the `KDFONTOP` ioctl on a virtual console device (`/dev/ttyN`, `/dev/tty`), reached through `vt_ioctl()`/`con_font_op()`; there is no network, packet, or remote-peer input into this code.\nAC:L - The attacker supplies every operand of the faulty arithmetic \u2014 `width`, `height` and `charcount` come straight from the user-provided `struct console_font_op` \u2014 and the allocation-then-copy sequence is a single deterministic ioctl with no race to win, no memory grooming and no state the attacker cannot set up.\nPR:L - `vt_ioctl()` grants `perm` to any process whose controlling terminal is the VT, so an ordinary unprivileged user logged in on a virtual console (physical console, embedded/automotive/kiosk fbcon system, or a serial/VT login) can issue `KD_FONT_OP_SET` without any capability; only the alternative `CAP_SYS_TTY_CONFIG` route needs real root.\nUI:N - The attacker performs the ioctl on its own console session; no administrator or second user has to open a file, mount anything, or take any action.\nS:U - The undersized allocation and the overflowing copy both occur in kernel heap memory within the same security authority the attacker is already attacking; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - A short kmalloc chunk followed by a length-mismatched copy loop corrupts adjacent slab objects, and the font is subsequently readable back via `KD_FONT_OP_GET`/`con_font_get()`, so out-of-bounds heap contents \u2014 kernel pointers, credentials, other slab users\u0027 data \u2014 can be disclosed to userspace.\nI:H - The overflow is an out-of-bounds heap write whose length and byte content are entirely attacker-chosen (the glyph bitmap), which is the classic primitive for overwriting neighbouring slab objects such as function pointers or `struct cred`, giving arbitrary modification and potential control-flow hijack.\nA:H - Writing past the end of the font allocation corrupts the slab and reliably produces a kernel oops, SLUB freelist BUG, or panic; the ioctl can be repeated at will, so it is a repeatable full-system denial of service."
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                  "status": "unaffected",
                  "version": "5.10.245",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.15.*",
                  "status": "unaffected",
                  "version": "5.15.194",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.1.*",
                  "status": "unaffected",
                  "version": "6.1.155",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.6.*",
                  "status": "unaffected",
                  "version": "6.6.109",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.12.*",
                  "status": "unaffected",
                  "version": "6.12.50",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.16.*",
                  "status": "unaffected",
                  "version": "6.16.10",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "6.17",
                  "versionType": "original_commit_for_fix"
                }
              ]
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.4.300",
                      "versionStartIncluding": "5.4.62",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.10.245",
                      "versionStartIncluding": "5.9",
                      "vulnerable": true
                    },
                    {
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                    {
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                      "versionEndExcluding": "6.12.50",
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                    {
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                      "versionStartIncluding": "5.9",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.17",
                      "versionStartIncluding": "5.9",
                      "vulnerable": true
                    },
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                      "versionStartIncluding": "4.4.235",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "4.9.235",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "4.14.196",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "4.19.143",
                      "vulnerable": true
                    },
                    {
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                      "versionStartIncluding": "5.8.6",
                      "vulnerable": true
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                  ],
                  "negate": false,
                  "operator": "OR"
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            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfbcon: fix integer overflow in fbcon_do_set_font\n\nFix integer overflow vulnerabilities in fbcon_do_set_font() where font\nsize calculations could overflow when handling user-controlled font\nparameters.\n\nThe vulnerabilities occur when:\n1. CALC_FONTSZ(h, pitch, charcount) performs h * pith * charcount\n   multiplication with user-controlled values that can overflow.\n2. FONT_EXTRA_WORDS * sizeof(int) + size addition can also overflow\n3. This results in smaller allocations than expected, leading to buffer\n   overflows during font data copying.\n\nAdd explicit overflow checking using check_mul_overflow() and\ncheck_add_overflow() kernel helpers to safety validate all size\ncalculations before allocation."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "scenarios": [
                {
                  "lang": "en",
                  "value": "AV:L - The only route to `fbcon_set_font()` is the `KDFONTOP` ioctl on a virtual console device (`/dev/ttyN`, `/dev/tty`), reached through `vt_ioctl()`/`con_font_op()`; there is no network, packet, or remote-peer input into this code.\nAC:L - The attacker supplies every operand of the faulty arithmetic \u2014 `width`, `height` and `charcount` come straight from the user-provided `struct console_font_op` \u2014 and the allocation-then-copy sequence is a single deterministic ioctl with no race to win, no memory grooming and no state the attacker cannot set up.\nPR:L - `vt_ioctl()` grants `perm` to any process whose controlling terminal is the VT, so an ordinary unprivileged user logged in on a virtual console (physical console, embedded/automotive/kiosk fbcon system, or a serial/VT login) can issue `KD_FONT_OP_SET` without any capability; only the alternative `CAP_SYS_TTY_CONFIG` route needs real root.\nUI:N - The attacker performs the ioctl on its own console session; no administrator or second user has to open a file, mount anything, or take any action.\nS:U - The undersized allocation and the overflowing copy both occur in kernel heap memory within the same security authority the attacker is already attacking; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - A short kmalloc chunk followed by a length-mismatched copy loop corrupts adjacent slab objects, and the font is subsequently readable back via `KD_FONT_OP_GET`/`con_font_get()`, so out-of-bounds heap contents \u2014 kernel pointers, credentials, other slab users\u0027 data \u2014 can be disclosed to userspace.\nI:H - The overflow is an out-of-bounds heap write whose length and byte content are entirely attacker-chosen (the glyph bitmap), which is the classic primitive for overwriting neighbouring slab objects such as function pointers or `struct cred`, giving arbitrary modification and potential control-flow hijack.\nA:H - Writing past the end of the font allocation corrupts the slab and reliably produces a kernel oops, SLUB freelist BUG, or panic; the ioctl can be repeated at will, so it is a repeatable full-system denial of service."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T12:06:36.336Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/994bdc2d23c79087fbf7dcd9544454e8ebcef877"
            },
            {
              "url": "https://git.kernel.org/stable/c/9c8ec14075c5317edd6b242f1be8167aa1e4e333"
            },
            {
              "url": "https://git.kernel.org/stable/c/b8a6e85328aeb9881531dbe89bcd2637a06c3c95"
            },
            {
              "url": "https://git.kernel.org/stable/c/a6eb9f423b3db000aaedf83367b8539f6b72dcfc"
            },
            {
              "url": "https://git.kernel.org/stable/c/adac90bb1aaf45ca66f9db8ac100be16750ace78"
            },
            {
              "url": "https://git.kernel.org/stable/c/4a4bac869560f943edbe3c2b032062f6673b13d3"
            },
            {
              "url": "https://git.kernel.org/stable/c/c0c01f9aa08c8e10e10e8c9ebb5be01a4eff6eb7"
            },
            {
              "url": "https://git.kernel.org/stable/c/1a194e6c8e1ee745e914b0b7f50fa86c89ed13fe"
            }
          ],
          "title": "fbcon: fix integer overflow in fbcon_do_set_font",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2025-39967",
        "datePublished": "2025-10-15T07:55:51.554Z",
        "dateReserved": "2025-04-16T07:20:57.149Z",
        "dateUpdated": "2026-08-05T12:06:36.336Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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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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  • 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.


Detection rules are retrieved from Rulezet.


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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.