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CVE-2026-97876

Bypass of GRUB lockdown restriction in Secure Boot mode via serial command MMIO base address

6.4 MediumFix available

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled.

The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grub_file_verifiers list in a way that disables the subsequent verification of loaded modules.

Attack profile

How easy it is to exploit

Attack vector
Local
Complexity
High
Privileges needed
High
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

0.11%Unchanged since Oct 3, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.4

Bypass of GRUB lockdown restriction in Secure Boot mode via serial command MMIO base address

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled.

The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grub_file_verifiers list in a way that disables the subsequent verification of loaded modules.

Record
CVE-2026-97876
CVSS 3.1
6.4 MediumCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-822
Updated
2026-11-02
EUVDEUVD-2026-91376 6.4

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled.

The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grub_file_verifiers list in a way that disables the subsequent verification of loaded modules.

Record
EUVD-2026-91376
CVSS 3.1
6.4 MediumCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-v555-hf4g-q6pc 6.4

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when...

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled.

The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grub_file_verifiers list in a way that disables the subsequent verification of loaded modules.

Record
GHSA-v555-hf4g-q6pc
CVSS 3.1
6.4 MediumCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-822
Updated
2026-11-02
NVD 6.4

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled.

The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grub_file_verifiers list in a way that disables the subsequent verification of loaded modules.

Record
CVE-2026-97876
CVSS 3.1
6.4 MediumCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-822
Updated
2026-11-02
OSVBELL-CVE-2026-97876 6.4
Record
BELL-CVE-2026-97876
CVSS 3.1
6.4 MediumCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSV 6.4

Bypass of GRUB lockdown restriction in Secure Boot mode via serial command MMIO base address

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled.

The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grub_file_verifiers list in a way that disables the subsequent verification of loaded modules.

Record
CVE-2026-97876
CVSS 3.1
6.4 MediumCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-822
Updated
2026-11-02
OSVDEBIAN-CVE-2026-97876 6.4

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled. The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grub_file_verifiers list in a way that disables the subsequent verification of loaded modules.

Record
DEBIAN-CVE-2026-97876
CVSS 3.1
6.4 MediumCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2026-97876 6.4

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled. The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grub_file_verifiers list in a way that disables the subsequent verification of loaded modules.

Record
UBUNTU-CVE-2026-97876
CVSS 3.1
6.4 MediumCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
grub
Alpaquita:23
2.12-r0 up to 2.12-r9
2.12-r9
grub
Alpaquita:25
2.12-r10 up to 2.12-r12
2.12-r12
grub
Alpaquita:stream
2.12-r0 up to 2.14-r2
2.14-r2
grub2
Debian:13
All versions, plus listed versions
2.12-92.12-9+deb13u12.12-9+deb13u22.12-9+hurd.12.14-1
Show 6 moreShow less
2.14-22.14-32.14-42.14~git20250718.0e36779-12.14~git20250718.0e36779-22.16-1
None known
grub2
Debian:14
before 2.14-4, plus listed versions
2.12-92.12-9+hurd.12.14-12.14-22.14-32.14~git20250718.0e36779-12.14~git20250718.0e36779-2
2.14-4
grub2
Ubuntu:Pro:14.04:LTS
All versions, plus listed versions
2.00-19ubuntu22.00-19ubuntu32.00-19ubuntu42.00-202.00-21
Show 23 moreShow less
2.00-222.02~beta2-52.02~beta2-62.02~beta2-72.02~beta2-82.02~beta2-92.02~beta2-9ubuntu12.02~beta2-9ubuntu1.12.02~beta2-9ubuntu1.22.02~beta2-9ubuntu1.32.02~beta2-9ubuntu1.42.02~beta2-9ubuntu1.52.02~beta2-9ubuntu1.62.02~beta2-9ubuntu1.72.02~beta2-9ubuntu1.82.02~beta2-9ubuntu1.112.02~beta2-9ubuntu1.122.02~beta2-9ubuntu1.142.02~beta2-9ubuntu1.152.02~beta2-9ubuntu1.162.02~beta2-9ubuntu1.172.02~beta2-9ubuntu1.202.02~beta2-9ubuntu1.21
None known
grub2-signed
Ubuntu:Pro:14.04:LTS
All versions, plus listed versions
1.221.231.241.251.26
Show 23 moreShow less
1.271.301.311.321.331.341.34.11.34.21.34.31.34.41.34.51.34.61.34.71.34.81.34.91.34.131.34.141.34.161.34.171.34.181.34.201.34.221.34.24
None known
grub2-signed
Ubuntu:16.04:LTS
All versions, plus listed versions
1.551.561.571.581.59
Show 32 moreShow less
1.611.621.631.641.651.661.66.11.66.21.66.61.66.71.66.81.66.91.66.111.66.121.66.141.66.151.66.161.66.171.66.181.66.191.66.201.66.211.66.221.66.231.66.261.66.271.66.281.66.291.167~16.04.11.167~16.04.21.167~16.04.41.167~16.04.6
None known
grub2-unsigned
Ubuntu:16.04:LTS
All versions, plus listed versions
2.04-1ubuntu442.04-1ubuntu44.12.04-1ubuntu44.1.2
None known
grub2-signed
Ubuntu:18.04:LTS
All versions, plus listed versions
1.851.861.871.891.91
Show 27 moreShow less
1.921.931.93.11.93.21.93.31.93.41.93.51.93.71.93.81.93.101.93.111.93.131.93.141.93.151.93.161.93.181.93.191.93.201.93.211.93.221.93.241.167~18.04.11.167~18.04.31.167~18.04.51.173.2~18.04.11.187.2~18.04.11.187.3~18.04.1
None known
Show 11 moreShow less
Affected packages
PackageAffectedFixed
grub2-unsigned
Ubuntu:18.04:LTS
All versions, plus listed versions
2.04-1ubuntu442.04-1ubuntu44.12.04-1ubuntu44.1.22.04-1ubuntu47.42.06-2ubuntu142.06-2ubuntu14.1
None known
grub2-signed
Ubuntu:20.04:LTS
All versions, plus listed versions
1.1281.1291.1301.1311.133
Show 27 moreShow less
1.1341.1351.1361.1371.1381.1391.1401.1411.1421.142.11.142.31.142.41.142.51.142.61.142.81.142.91.142.101.142.111.1671.167.21.173.2~20.04.11.173.41.187.2~20.04.21.187.3~20.04.11.187.4~20.04.11.187.6~20.04.11.187.12~20.04
None known
grub2-unsigned
Ubuntu:20.04:LTS
All versions, plus listed versions
2.04-1ubuntu442.04-1ubuntu44.22.04-1ubuntu47.42.04-1ubuntu47.52.06-2ubuntu14
Show 4 moreShow less
2.06-2ubuntu14.12.06-2ubuntu14.22.06-2ubuntu14.42.06-2ubuntu14.8
None known
grub2-signed
Ubuntu:22.04:LTS
All versions, plus listed versions
1.1731.1741.1761.1771.178
Show 8 moreShow less
1.1791.1801.182~22.04.11.187.21.187.3~22.04.11.187.4~22.04.11.187.61.187.12
None known
grub2-unsigned
Ubuntu:22.04:LTS
All versions, plus listed versions
2.04-1ubuntu472.04-1ubuntu482.06-2ubuntu32.06-2ubuntu42.06-2ubuntu5
Show 8 moreShow less
2.06-2ubuntu62.06-2ubuntu72.06-2ubuntu102.06-2ubuntu142.06-2ubuntu14.12.06-2ubuntu14.22.06-2ubuntu14.42.06-2ubuntu14.8
None known
grub2-signed
Ubuntu:24.04:LTS
All versions, plus listed versions
1.1971.1991.2011.2021.202.21.202.5
None known
grub2-unsigned
Ubuntu:24.04:LTS
All versions, plus listed versions
2.12~rc1-10ubuntu42.12~rc1-12ubuntu22.12-1ubuntu12.12-1ubuntu72.12-1ubuntu7.12.12-1ubuntu7.3
None known
grub2-signed
Ubuntu:26.10
All versions, plus listed versions
1.215
None known
grub2-unsigned
Ubuntu:26.10
All versions, plus listed versions
2.14-2ubuntu1
None known
grub2-signed
Ubuntu:26.04:LTS
All versions, plus listed versions
1.2141.215
None known
grub2-unsigned
Ubuntu:26.04:LTS
All versions, plus listed versions
2.14~git20250718.0e36779-1ubuntu42.14-2ubuntu1
None known

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-97876 is a medium vulnerability (CVSS 6.4) in Gnu Grub2, published October 2, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.11%, the 1st percentile. Fixed in grub 2.12-r9.

References

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