UBUNTU-CVE-2026-68090: Medium severity ubuntu/linux vulnerability
In the Linux kernel, the following vulnerability has been resolved: debugobjects: Plug race against a concurrent OOM disable syzbot reported a puzzling splat: WARNING: kernel/time/hrtimer.c:443 at stubtimer+0xa/0x20 stubtimer() is installed as timer callback function in hrtimerfixupassertinit(), which is invoked when debugobjectassertinit() can't find a shadow object. In that case debug objects emits a warning about it before invoking the fixup. Though the provided console log lacks this warning and instead has the following a few seconds before the splat: ODEBUG: Out of memory. ODEBUG disabled So the object was looked up in debugobjectassertinit() and the lookup failed due a concurrent out of memory situation which disabled debug objects and freed the shadow objects: debugobjectassertinit() if (!debugobjectsenabled) return; obj = alloc(); if (!obj) { // Out of memory debugobjectsenabled = false; freeobjects(); obj = lookuporalloc(); // The lookup failed because the other side // removed the objects, so this returns // an error code as the object in question // is not statically initialized if (!ISERRORNULL(obj)) return; if (!obj) { debugoom(); return; } print(...) if (!debugobjectsenabled) return; fixup(...) The debug object splat is skipped because debugobjectsenabled is false, but the fixup callback is invoked unconditionally, which makes the timer disfunctional. This is only a problem in debugobjectassertinit() and debugobjectactivate() as both have to handle statically initialized objects and therefore must handle the error pointer return case gracefully. All other places only handle the found/not found case and the NULL pointer return is a signal for OOM. Otherwise they get a valid shadow object. Plug the hole by checking whether debug objects are still enabled before invoking the print and fixup function in those two places.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1117.124~20.04.1 - Upgrade
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ubuntu/linux-lowlatencyto a version that resolves this vulnerability.Fixed in 5.15.0-195.205 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 6.8.0-1067.70 - Upgrade
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ubuntu/linux-aws-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1012.12~24.04.1 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79 - Upgrade
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ubuntu/linux-bluefieldto a version that resolves this vulnerability.Fixed in 6.8.0-1033.38 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1067.70+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-147.147+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-31.31 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1012.12 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1011.11 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1006.7 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 7.0.0-1018.18 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1011.11 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-31.31.1 - Compensating control
In the Linux kernel, in debug_object_assert_init() and debug_object_activate(), check whether debug objects are still enabled before invoking the print and fixup functions; skip both when debug_objects_enabled is false.
Event History
Frequently Asked Questions
What runtime conditions trigger the race?
The race occurs when debug object handling is concurrently disabled due to an out-of-memory condition while debug_object_assert_init() is looking up or allocating a shadow object. Disabling debug objects frees shadow objects, allowing the lookup to fail during the assertion path.
What signs could indicate this issue has occurred?
Relevant kernel log messages include “ODEBUG: Out of memory. ODEBUG disabled” followed by a warning involving kernel/time/hrtimer.c:443, stub_timer(), or hrtimer_fixup_assert_init().
Does the available information establish attacker prerequisites or a workaround when updates cannot be applied?
No. The provided information describes an internal race associated with out-of-memory handling and debug objects, but does not specify attacker access requirements, affected default configurations, or mitigations.