Apr 10, 2024NewsroomHardware Security / Linux

Cybersecurity researchers have disclosed what they say is the “first native Spectre v2 exploit” against the Linux kernel on Intel systems that could be exploited to read sensitive data from the memory.

The exploit, called Native Branch History Injection (BHI), can be used to leak arbitrary kernel memory at 3.5 kB/sec by bypassing existing Spectre v2/BHI mitigations, researchers from Systems and Network Security Group (VUSec) at Vrije Universiteit Amsterdam said in a new study.

The shortcoming is being tracked as CVE-2024-2201.

BHI was first disclosed by VUSec in March 2022, describing it as a technique that can get around Spectre v2 protections in modern processors from Intel, AMD, and Arm.

While the attack leveraged extended Berkeley Packet Filters (eBPFs), Intel’s recommendations to address the problem, among other things, were to disable Linux’s unprivileged eBPFs.

“Privileged managed runtimes that can be configured to allow an unprivileged user to generate and execute code in a privileged domain — such as Linux’s ‘unprivileged eBPF’ — significantly increase the risk of transient execution attacks, even when defenses against intra-mode [Branch Target Injection] are present,” Intel said at the time.

“The kernel can be configured to deny access to unprivileged eBPF by default, while still allowing administrators to enable it at runtime where needed.”

Native BHI neutralizes this countermeasure by showing that BHI is possible without eBPF. It impacts all Intel systems that are susceptible to BHI.

As a result, it makes it feasible for an attacker with access to CPU resources to influence speculative execution paths via malicious software installed on a machine with the goal of extracting sensitive data that are associated with a different process.

“Existing mitigation techniques of disabling privileged eBPF and enabling (Fine)IBT are insufficient in stopping BHI exploitation against the kernel/hypervisor,” the CERT Coordination Center (CERT/CC) said in an advisory.

“An unauthenticated attacker can exploit this vulnerability to leak privileged memory from the CPU by speculatively jumping to a chosen gadget.”

The flaw has been confirmed to affect Illumos, Intel, Red Hat, SUSE Linux, Triton Data Center, and Xen. AMD, in a bulletin, said it’s “aware of any impact” on its products.

The disclosure comes weeks after IBM and VUSec detailed GhostRace (CVE-2024-2193), a variant of Spectre v1 that employs a combination of speculative execution and race conditions to leak data from contemporary CPU architectures.

It also follows new research from ETH Zurich that disclosed a family of attacks dubbed Ahoi Attacks that could be used to compromise hardware-based trusted execution environments (TEEs) and break confidential virtual machines (CVMs) like AMD Secure Encrypted Virtualization-Secure Nested Paging (SEV-SNP) and Intel Trust Domain Extensions (TDX).

The attacks, codenamed Heckler and WeSee, make use of malicious interrupts to break the integrity of CVMs, potentially allowing threat actors to remotely log in and gain elevated access, as well as perform arbitrary read, write, and code injection to disable firewall rules and open a root shell.

“For Ahoi Attacks, an attacker can use the hypervisor to inject malicious interrupts to the victim’s vCPUs and trick it into executing the interrupt handlers,” the researchers said. “These interrupt handlers can have global effects (e.g., changing the register state in the application) that an attacker can trigger to compromise the victim’s CVM.”

In response to the findings, AMD said the vulnerability is rooted in the Linux kernel implementation of SEV-SNP and that fixes addressing some of the issues have been upstreamed to the main Linux kernel.

Jan 29, 2024NewsroomVulnerability / NTML Security

A now-patched security flaw in Microsoft Outlook could be exploited by threat actors to access NT LAN Manager (NTLM) v2 hashed passwords when opening a specially crafted file.

The issue, tracked as CVE-2023-35636 (CVSS score: 6.5), was addressed by the tech giant as part of its Patch Tuesday updates for December 2023.

“In an email attack scenario, an attacker could exploit the vulnerability by sending the specially crafted file to the user and convincing the user to open the file,” Microsoft said in an advisory released last month.

In a web-based attack scenario, an attacker could host a website (or leverage a compromised website that accepts or hosts user-provided content) containing a specially crafted file designed to exploit the vulnerability.”

Put differently, the adversary would have to convince users to click a link, either embedded in a phishing email or sent via an instant message, and then deceive them into opening the file in question.

CVE-2023-35636 is rooted in the calendar-sharing function in the Outlook email application, wherein a malicious email message is created by inserting two headers “Content-Class” and “x-sharing-config-url” with crafted values in order to expose a victim’s NTLM hash during authentication.

Varonis security researcher Dolev Taler, who has been credited with discovering and reporting the bug, said NTLM hashes could be leaked by leveraging Windows Performance Analyzer (WPA) and Windows File Explorer. These two attack methods, however, remain unpatched.

“What makes this interesting is that WPA attempts to authenticate using NTLM v2 over the open web,” Taler said.

“Usually, NTLM v2 should be used when attempting to authenticate against internal IP-address-based services. However, when the NTLM v2 hash is passing through the open internet, it is vulnerable to relay and offline brute-force attacks.”

The disclosure comes as Check Point revealed a case of “forced authentication” that could be weaponized to leak a Windows user’s NTLM tokens by tricking a victim into opening a rogue Microsoft Access file.

Microsoft, in October 2023, announced plans to discontinue NTLM in Windows 11 in favor of Kerberos for improved security owing to the fact that it does not support cryptographic methods and is susceptible to relay attacks.