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Rowhammer is an increasingly threatening vulnerability that grants an attacker the ability to flip bits in memory without directly accessing them. Despite efforts to mitigate Rowhammer via software and defenses built directly into DRAM modules, more recent generations of DRAM are actually more susceptible to malicious bit-flips than their predecessors. This phenomenon has spawned numerous exploits, showing how Rowhammer acts as the basis for various vulnerabilities that target sensitive structures, such as Page Table Entries (PTEs) or opcodes, to grant control over a victim machine. However, in this paper, we consider Rowhammer as a more general vulnerability, presenting a novel exploit vector for Rowhammer that targets particular code patterns. We show that if victim code is designed to return benign data to an unprivileged user, and uses nested pointer dereferences, Rowhammer can flip these pointers to gain arbitrary read access in the victim's address space. Furthermore, we identify gadgets present in the Linux kernel, and demonstrate an end-to-end attack that precisely flips a targeted pointer. To do so we developed a number of improved Rowhammer primitives, including kernel memory massaging, Rowhammer synchronization, and testing for kernel flips, which may be of broader interest to the Rowhammer community. Compared to prior works' leakage rate of .3 bits/s, we show that such gadgets can be used to read out kernel data at a rate of 82.6 bits/s. By targeting code gadgets, this work expands the scope and attack surface exposed by Rowhammer. It is no longer sufficient for software defenses to selectively pad previously exploited memory structures in flip-safe memory, as any victim code that follows the pattern in question must be protected.
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SCAVY: Automated Discovery of Memory Corruption Targets in Linux Kernel for Privilege Escalation
Kernel privilege-escalation exploits typically leverage memory-corruption vulnerabilities to overwrite particular target locations. These memory corruption targets play a critical role in the exploits, as they determine which privileged resources (e.g., files, memory, and operations) the adversary may access and what privileges (e.g., read, write, and unrestricted) they may gain. While prior research has made important advances in discovering vulnerabilities and achieving privilege escalation, in practice, the exploits rely on the few memory corruption targets that have been discovered manually so far. We propose SCAVY, a framework that automatically discovers memory corruption targets for privilege escalation in the Linux kernel. SCAVY's key insight lies in broadening the search scope beyond the kernel data structures explored in prior work, which focused on function pointers or pointers to structures that include them, to encompass the remaining 90% of Linux kernel structures. Additionally, the search is bug-type agnostic, as it considers any memory corruption capability. To this end, we develop novel and scalable techniques that combine fuzzing and differential analysis to automatically explore and detect privilege escalation by comparing the accessibility of resources between executions with and without corruption. This allows SCAVY to determine that corrupting a certain field puts the system in an exploitable state, independently of the vulnerability exploited. SCAVY found 955 PoC, from which we identify 17 new fields in 12 structures that can enable privilege escalation. We utilize these targets to develop 6 exploits for 5 CVE vulnerabilities. Our findings show that new memory corruption targets can change the security implications of vulnerabilities, urging researchers to proactively discover memory corruption targets.
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- PAR ID:
- 10547054
- Editor(s):
- Balzarotti, Davide; Xu, Wenyuan
- Publisher / Repository:
- USENIX Association
- Date Published:
- ISSN:
- 978-1-939133-44-1
- ISBN:
- 978-1-939133-44-1
- Page Range / eLocation ID:
- 7141--7158
- Format(s):
- Medium: X
- Location:
- Philladelphia, PA
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
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- The DOI is not currently available.
