200 lines
12 KiB
JSON
200 lines
12 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2025-39821",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2025-04-16T07:20:57.139Z",
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"datePublished": "2025-09-16T13:00:20.805Z",
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"dateUpdated": "2026-08-05T12:05:25.973Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-08-05T12:05:25.973Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nperf: Avoid undefined behavior from stopping/starting inactive events\n\nCalling pmu->start()/stop() on perf events in PERF_EVENT_STATE_OFF can\nleave event->hw.idx at -1. When PMU drivers later attempt to use this\nnegative index as a shift exponent in bitwise operations, it leads to UBSAN\nshift-out-of-bounds reports.\n\nThe issue is a logical flaw in how event groups handle throttling when some\nmembers are intentionally disabled. Based on the analysis and the\nreproducer provided by Mark Rutland (this issue on both arm64 and x86-64).\n\nThe scenario unfolds as follows:\n\n 1. A group leader event is configured with a very aggressive sampling\n period (e.g., sample_period = 1). This causes frequent interrupts and\n triggers the throttling mechanism.\n 2. A child event in the same group is created in a disabled state\n (.disabled = 1). This event remains in PERF_EVENT_STATE_OFF.\n Since it hasn't been scheduled onto the PMU, its event->hw.idx remains\n initialized at -1.\n 3. When throttling occurs, perf_event_throttle_group() and later\n perf_event_unthrottle_group() iterate through all siblings, including\n the disabled child event.\n 4. perf_event_throttle()/unthrottle() are called on this inactive child\n event, which then call event->pmu->start()/stop().\n 5. The PMU driver receives the event with hw.idx == -1 and attempts to\n use it as a shift exponent. e.g., in macros like PMCNTENSET(idx),\n leading to the UBSAN report.\n\nThe throttling mechanism attempts to start/stop events that are not\nactively scheduled on the hardware.\n\nMove the state check into perf_event_throttle()/perf_event_unthrottle() so\nthat inactive events are skipped entirely. This ensures only active events\nwith a valid hw.idx are processed, preventing undefined behavior and\nsilencing UBSAN warnings. The corrected check ensures true before\nproceeding with PMU operations.\n\nThe problem can be reproduced with the syzkaller reproducer:"
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 7.8,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:L - The vulnerability is reached exclusively through the `perf_event_open(2)` syscall and `ioctl(PERF_EVENT_IOC_PERIOD)` on the resulting fd; there is no network or remote-peer input path into the perf throttling code.\nAC:L - The attacker fully controls both halves — the group leader's `sample_period=1` deterministically forces throttling within milliseconds, and the disabled sibling is created by the attacker; there is no race or memory-layout condition outside their influence, and the UAF window length is itself chosen via the sibling's `sample_period`.\nPR:L - At the mainline default `kernel.perf_event_paranoid=2`, an unprivileged local user can open a task-scoped sampling group with `exclude_kernel=1` and no capabilities (`perf_allow_kernel()` is only invoked for `!exclude_kernel`), and software cpu-clock/task-clock events need no hardware PMU, so the bug is reachable from containers and VMs.\nUI:N - The attacking process performs the entire sequence — create group, force throttle, wait for unthrottle, close the fds — with no action by any other user or victim process.\nS:U - The corruption is confined to kernel memory and PMU state within the same security authority; no hypervisor, IOMMU, or sandbox boundary is crossed.\nC:H - A `perf_event` is freed while its embedded `hw.hrtimer` remains enqueued on the per-CPU hrtimer base, giving a use-after-free over an attacker-timed window that can be reclaimed and read back through the timer machinery; the x86 path additionally performs an out-of-bounds `bt` read below `cpuc->active_mask`.\nI:H - The dangling hrtimer means `__run_hrtimer()` calls `timer->function` from reclaimed heap memory, a direct control-flow hijack primitive after a heap spray; the x86 `btr` at bit offset -1 is also an out-of-bounds bit write into the adjacent per-CPU `cpu_hw_events` pointer.\nA:H - Even without exploitation the bug reliably produces kernel oopses from the freed-timer dereference, and the arm64 path hits a non-`_ONCE` `WARN(1, \"Invalid PMEV* index\")` plus a UBSAN shift-out-of-bounds report on every trigger — an unprivileged panic under `panic_on_warn`/`ubsan_panic` and log flooding otherwise."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"kernel/events/core.c"
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],
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"versions": [
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{
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"version": "9734e25fbf5ae68eb04234b2cd14a4b36ab89141",
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"lessThan": "d689135aa9c5e4e0eab5a92bbe35dab0c8d6677f",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "9734e25fbf5ae68eb04234b2cd14a4b36ab89141",
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"lessThan": "b64fdd422a85025b5e91ead794db9d3ef970e369",
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"status": "affected",
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"versionType": "git"
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}
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]
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},
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "affected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"kernel/events/core.c"
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],
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"versions": [
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{
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"version": "6.16",
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"status": "affected"
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},
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{
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"version": "0",
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"lessThan": "6.16",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.16.5",
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"lessThanOrEqual": "6.16.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.17",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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}
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]
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}
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],
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"cpeApplicability": [
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{
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"nodes": [
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{
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"operator": "OR",
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"negate": false,
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"cpeMatch": [
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.16",
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"versionEndExcluding": "6.16.5"
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},
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.16",
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"versionEndExcluding": "6.17"
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}
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]
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}
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]
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}
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],
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"references": [
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{
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"url": "https://git.kernel.org/stable/c/d689135aa9c5e4e0eab5a92bbe35dab0c8d6677f"
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},
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{
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"url": "https://git.kernel.org/stable/c/b64fdd422a85025b5e91ead794db9d3ef970e369"
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}
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],
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"title": "perf: Avoid undefined behavior from stopping/starting inactive events",
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"x_generator": {
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"engine": "bippy-1.2.0"
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}
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},
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"adp": [
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{
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"metrics": [
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{
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"cvssV3_1": {
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"scope": "UNCHANGED",
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"version": "3.1",
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"baseScore": 7.8,
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"attackVector": "LOCAL",
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"baseSeverity": "HIGH",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"integrityImpact": "HIGH",
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"userInteraction": "NONE",
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"attackComplexity": "LOW",
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"availabilityImpact": "HIGH",
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"privilegesRequired": "LOW",
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"confidentialityImpact": "HIGH"
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}
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},
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{
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"other": {
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"type": "ssvc",
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"content": {
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"id": "CVE-2025-39821",
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"role": "CISA Coordinator",
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"options": [
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{
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"Exploitation": "none"
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},
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{
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"Automatable": "no"
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},
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{
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"Technical Impact": "total"
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}
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],
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"version": "2.0.3",
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"timestamp": "2026-01-14T18:16:47.835074Z"
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}
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}
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}
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],
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"problemTypes": [
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{
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"descriptions": [
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{
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"lang": "en",
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"type": "CWE",
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"cweId": "CWE-787",
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"description": "CWE-787 Out-of-bounds Write"
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}
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]
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}
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],
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"title": "CISA ADP Vulnrichment",
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"providerMetadata": {
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"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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"shortName": "CISA-ADP",
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"dateUpdated": "2026-01-14T18:22:56.192Z"
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}
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}
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]
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}
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} |