MediumPublic exploit

Secure Boot bypass via insecure default UEFI Shell enablement in Ubuntu EDK2

IdentifiersCVE-2023-48733CWE-1188· Initialization of a Resource with…

CVE-2023-48733 is an insecure-default configuration issue in Ubuntu's EDK2 build where UEFI Shell support was left enabled. Because the shell is available in a Secure Boot trust context, an attacker with OS-level access can invoke shell functionality to undermine the Secure Boot chain of trust and bypass boot-time verification. The provided context ties this class of issue to signed UEFI shell environments that expose powerful functionality such as direct memory modification, allowing security checks to be altered before the operating system boots. In practical terms, this enables modification of boot-time state so that unsigned or malicious pre-OS code can be loaded despite Secure Boot appearing enabled.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows bypass of Secure Boot, defeating a core platform integrity control. An attacker who already has code execution on the installed OS can transition that access into pre-boot compromise, load arbitrary unsigned boot components, and establish persistence below the operating system. This can enable stealthy malware or bootkits that survive reboots, evade many OS-level defenses, and maintain the appearance of a normally secured system while firmware or boot-chain trust has been subverted.

Mitigation

If you can’t patch tonight, do this now.

Until full remediation is deployed, restrict the ability to boot or invoke UEFI Shell, protect firmware settings with a BIOS/UEFI password, and tightly control administrative/root access on the OS since the issue is OS-resident attacker exploitable. Use custom Secure Boot keys where operationally feasible, keep DBX revocation lists current, and scan systems for vulnerable signed UEFI components. Limit physical and privileged local access to reduce opportunities to abuse pre-boot tooling.

Remediation

Patch, then assume compromise.

Apply vendor-provided updates for Ubuntu/EDK2 and any affected platform firmware that disable or remove the insecure UEFI Shell default in Secure Boot contexts. Where available, install updated BIOS/UEFI firmware and updated Secure Boot DBX revocation lists to block known-vulnerable signed shell binaries. Replace affected signed UEFI shell binaries with corrected versions that do not permit this bypass path, and follow vendor guidance for revoking previously trusted vulnerable components.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

CanonicalLxdapplication

DebianDebian Linuxoperating_system

TianocoreEdk2application

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

2 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

2 SOURCESView more in app

eclypsium blogNews

Oct 14, 2025

BombShell: The Signed Backdoor Hiding in Plain Sight on Framework Devices

An insecure UEFI Shell in EDK2, left enabled in Ubuntu’s EDK2, allows attackers to bypass Secure Boot protections.

What this page doesn’t show

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity1