Highly exploitable, CVE-2026-89762 poses a critical security risk that could lead to severe breaches.
Status: Received on 11 Sep 2026, 20:20 UTC
Last updated: 🕖 13 Sep 2026, 07:17 UTC
Originally published on: 🕗 11 Sep 2026, 20:20 UTC
Time between publication and last update: 1 days
CVSS Release: version 3
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Secondary
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVE-2026-89762: In the Linux kernel, the following vulnerability has been resolved: apparmor: fix cred UAF caused by begin_current_label_crit_section() AppArmor's begin_current_label_crit_section() is a scary function called from lots of LSM hooks (in particular VFS/socket-related ones) that checks if the label referenced by the current creds is marked FLAG_STALE, and if so, attempts to use aa_replace_current_label() to replace the creds with an updated version that uses a new label. The first problem with this is that it would directly lead to UAF of `struct cred` if anything in the kernel takes a pointer to the current creds and accesses these past a security hook invocation that replaces creds, like so: ``` const struct cred *cred = current_cred(); alloc_file_pseudo(...); uid_t uid = cred->euid; ``` I don't know if anything in the kernel actually does this, but I think it is very surprising that this pattern could lead to UAF. The second problem is that things go wrong when aa_replace_current_label() runs with overridden credentials. aa_replace_current_label() bails out if `current_cred() != current_real_cred()` (mirroring the check in proc_pid_attr_write()), but this check can't actually reliably detect overridden credentials because the overridden creds can be the same as the objective creds. So in approximately the following scenario, things go wrong: 1. task begins with <creds A> (as both objective and subjective creds), with refcount=2 2. task grabs an extra reference on <creds A> for overriding 3. task calls override_creds(<creds A>), which returns a pointer to the old subjective creds (<creds A>) 4. task enters AppArmor LSM hook 5. AppArmor checks that objective/subjective creds are equal 6. AppArmor replaces both cred pointers with <creds B> and drops 2 refs on <creds A> 7. task leaves AppArmor LSM hook 8. task calls revert_creds(<creds A>) 9. now task->cred is <creds A> while task->real_cred is <creds B>, but the task_struct logically holds two references to <creds B> 10. another task drops the extra reference on <creds A> that was used for overriding, refcount drops to 0 11. now task->real_cred points to freed creds At this point, any access to current_cred() will be UAF. I have a test case where I run aa-disable on a profile while a process using that profile is blocked on splice() from a FUSE passthrough file into a full pipe; after the profile update, the pipe becomes empty, splice() resumes, the credentials go out of sync, and a subsequent getuid() syscall results in a KASAN UAF splat. To fix this, instead of directly replacing creds, do it via task_work that will run at the end of the current syscall. (The point in time at which the cred replacement happens should have no correctness impact; it is just a performance optimization to avoid unnecessarily touching the refcount of the new label.) Note that AppArmor still performs direct cred replacements in the sb_pivotroot LSM hook after this change, and that direct cred replacements can still happen in VFS ->write() callbacks via proc_pid_attr_write(). There are two options for what to do with aa_dup_task_ctx(): Either explicitly reset new->label_replacement_pending after the entire aa_task_ctx has been copied, or switch to manually copying members over. I am switching to manually copying members over because that should make bugs more obvious.
The exploitability of CVE-2026-89762 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).
CVE-2026-89762 presents an accessible attack vector with minimal effort required. Restricting access controls and implementing security updates are critical to reducing exploitation risks.
A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.
Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.
Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.
Above is the CVSS Sub-score Breakdown for CVE-2026-89762, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.
Below is the Impact Analysis for CVE-2026-89762, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.
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