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Unrated severityNVD Advisory· Published Mar 3, 2021· Updated Aug 4, 2024

CVE-2020-27749

CVE-2020-27749

Description

A stack buffer overflow in grub2's command line parser allows local attackers to bypass Secure Boot protections via a crafted variable expansion.

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

A stack buffer overflow in grub2's command line parser allows local attackers to bypass Secure Boot protections via a crafted variable expansion.

Vulnerability

The vulnerability resides in the grub_parser_split_cmdline() function of GRUB2 versions prior to 2.06. This function expands variable names referenced in the command line into their corresponding contents using a 1kB stack buffer without sufficient bounds checking. If a variable with a sufficiently large payload is referenced, it can overflow the stack buffer, corrupt the stack frame, and allow control flow hijacking.

Exploitation

An attacker with local access or the ability to modify boot configuration (e.g., by editing GRUB configuration files) can craft a command line that references a variable containing a large payload. When the system boots, the vulnerable function processes this input, triggering a stack buffer overflow. This can corrupt the stack and gain arbitrary code execution.

Impact

Successful exploitation grants arbitrary code execution at the firmware level, allowing an attacker to bypass Secure Boot protections. This compromises the integrity and confidentiality of the system, and can lead to persistent, stealthy malware installation or denial of service.

Mitigation

The vulnerability is fixed in GRUB2 version 2.06. Gentoo users should upgrade to >=sys-devel/grub-2.06_rc1 [3]. Red Hat has released patches for certain Enterprise Linux versions [1]. After upgrading, administrators must run grub-install to apply the fix. No workaround is available; upgrading the bootloader is necessary.

References
  1. Stack buffer overflow in grub_parser_split_cmdline()
  2. Multiple vulnerabilities (GLSA 202104-05) — Gentoo security

AI Insight generated on May 26, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected products

41

Patches

0

No patches discovered yet.

Vulnerability mechanics

No source-code context for this CVE — mechanics is only generated when we can read the actual fix diff. Without that, the four sections (root cause, attack vector, affected code, fix) would be speculation rather than analysis.

References

4

News mentions

0

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