Linux Kernel up to 6.18.50/7.2.4 KVM pgshift_level_to_ttl signed conversion

CVSS Meta Temp Score
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CTI Interest Score
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9.5$0-$5k0.90

Summaryinfo

A vulnerability marked as very critical has been reported in Linux Kernel up to 6.18.50/7.2.4. The impacted element is the function pgshift_level_to_ttl of the component KVM. This manipulation causes signed conversion. This vulnerability is tracked as CVE-2026-89775. The attack is possible to be carried out remotely. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as very critical was found in Linux Kernel up to 6.18.50/7.2.4. Affected by this vulnerability is the function pgshift_level_to_ttl of the component KVM. The manipulation with an unknown input leads to a signed conversion vulnerability. The CWE definition for the vulnerability is CWE-195. The product uses a signed primitive and performs a cast to an unsigned primitive, which can produce an unexpected value if the value of the signed primitive can not be represented using an unsigned primitive. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Handle negative S1 walk levels in VNCR TLB size evaluation Computing the effects of a TLB invalidation involves looking at the size of the mapping cached by the TLB. For S1 mappings such as VNCR, this is deducted from the combination of the base granule size and the mapping level. However, this implies that the S1 MMU is *on*. When the MMU is off, we indicate this with the level being set to a "creative" value of -127 (S1_MMU_DISABLED). This ends-up being misinterpreted by pgshift_level_to_ttl() as it doesn't handle negative levels at all (the level is immediately cast to a u8 and only the bottom two bits considered), leading to an invalidation size of 0. Not helpful. Tidy-up pgshift_level_to_ttl() to handle these negative levels, and ttl_to_size() to always return SZ_1G when no valid TTL is present. This allows the removal of open-coded checks for similar situations. Note that the check for a negative value not explicitely checking for S1_MMU_DISABLED is deliberate, so that actual negative levels introduced with LVA2 and D128 can take the same path if we ever support them.

The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2026-89775 since 09/11/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/16/2026).

Upgrading to version 6.18.51, 7.2.5 or 7.3-rc1 eliminates this vulnerability. Applying the patch be54a70067c7dbe1381157e8a238fa4b16ea9c05/1c9fca34b9625a67a7f1a03c8604f3df760c6c49/8053393680d4fa3eb962667d2be95dd39f0940e5 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 9.9
VulDB Meta Temp Score: 9.5

VulDB Base Score: 9.9
VulDB Temp Score: 9.5
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Signed conversion
CWE: CWE-195 / CWE-194 / CWE-189
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.18.51/7.2.5/7.3-rc1
Patch: be54a70067c7dbe1381157e8a238fa4b16ea9c05/1c9fca34b9625a67a7f1a03c8604f3df760c6c49/8053393680d4fa3eb962667d2be95dd39f0940e5

Timelineinfo

09/11/2026 CVE reserved
09/16/2026 +5 days Advisory disclosed
09/16/2026 +0 days VulDB entry created
09/16/2026 +0 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-89775 (🔒)
GCVE (CVE): GCVE-0-2026-89775
GCVE (VulDB): GCVE-100-405577

Entryinfo

Created: 09/16/2026 11:14
Changes: 09/16/2026 11:14 (59)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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