CVE-2017-1000253

What Is the Linux Kernel ELF Loader?

The Linux kernel's ELF (Executable and Linkable Format) loader is the component responsible for mapping executable files into process memory when a program is launched via exec(). The loader (load_elf_binary() in fs/binfmt_elf.c) parses ELF headers to determine where to map code, data, BSS (uninitialized data), stack, and any interpreter (dynamic linker). Position-Independent Executables (PIE) are ELF binaries compiled to run at any memory address, enabling ASLR — the kernel chooses the load address at runtime. Errors in PIE layout accounting can cause the kernel to map the stack overlapping with the loaded binary, corrupting the stack with data from the BSS segment.

Overview

CVE-2017-1000253 is a stack buffer corruption vulnerability in the Linux kernel's ELF loader (load_elf_binary()) that allows a local attacker with a standard user account to escalate privileges to root. When the kernel maps a PIE binary with a large BSS segment, it fails to account for the interpreter stack space when calculating the load address, causing the program stack to be mapped overlapping with the BSS segment. This stack corruption can be exploited to achieve arbitrary code execution in kernel context. Published in October 2017 after Qualys researchers developed working exploits for CentOS 7 and RHEL 7. Added to the CISA KEV catalog in September 2024 reflecting ransomware operators' use of this vulnerability to escalate from user to root on compromised Linux systems. CISA's ransomwareUse: true flag reflects its incorporation into post-exploitation toolkits targeting Linux servers.

Affected Versions

Technical Details

Root Cause: PIE Stack Mapping Overlap in load_elf_binary()

CVE-2017-1000253 is a memory buffer vulnerability (CWE-119) in load_elf_binary() in the Linux kernel's ELF binary loader (fs/binfmt_elf.c). The bug involves incorrect accounting of stack space when loading PIE executables:

Vulnerability mechanics:

1. When loading a PIE binary, load_elf_binary() must choose a load address for the binary in the process address space
2. The function calculates whether there is space to load both the binary and the interpreter (ld-linux.so) stack below it
3. The calculation fails to account for the additional stack space needed by the ELF interpreter itself on systems where PIE is enabled by default
4. When the BSS segment of a PIE binary is large, the kernel maps the program stack overlapping the BSS segment
5. Data written to BSS by program initialization overwrites stack return addresses and saved registers, leading to corruption that can be exploited for arbitrary code execution

Exploitation severity: Qualys developed reliable proof-of-concept exploits for CentOS 7 and RHEL 7, demonstrating that a local unprivileged user could achieve root within seconds. The attack requires only that the attacker can execute a binary on the target system — no special environment or privileges needed beyond a valid user account.

Why RHEL/CentOS 7 was particularly affected: Red Hat compiled many system binaries as PIE by default in RHEL 7 — including su and other SUID binaries — which had large enough BSS segments to trigger the overlap condition reliably.

Attack Characteristics

Discovery

Qualys researchers discovered and published CVE-2017-1000253 in September 2017 with a full technical writeup and proof-of-concept exploit targeting CentOS 7 and RHEL 7. The fix was submitted by Michael Davidson and merged as kernel commit a87938b2e246b81b4fb713edb371a9fa3c5c3c86.

Exploitation Context

• Ransomware post-exploitation on Linux: The ransomwareUse: true classification reflects that ransomware operators targeting Linux servers (ESXi hosts, NAS devices, file servers) incorporate LPE vulnerabilities like CVE-2017-1000253 into their toolkits — initial access is often via web application exploitation or stolen credentials at user level, then LPE achieves root for full system encryption
• Long KEV lag: The seven-year gap between the 2017 patch and the 2024 KEV addition reflects the real-world persistence of unpatched Linux kernels in production — long-running containers, embedded systems, and legacy server deployments frequently run years-old kernels; CISA's 2024 addition confirmed ransomware operators were actively exploiting unpatched RHEL 7 / CentOS 7 systems
• CentOS 7 end of life: CentOS 7 reached end of life on June 30, 2024 — right before CISA added this to KEV — meaning many organizations still running CentOS 7 infrastructure have no further upstream patches and are exposed to this and all subsequent unpatched kernel vulnerabilities
• Common open-source component: The CISA KEV entry notes this is "a common open-source component, third-party library, or a protocol used by different products" — the vulnerability affected any Linux-based product running a vulnerable 3.10.x kernel, including network appliances, cloud infrastructure, and embedded Linux devices

Remediation

1. Update the Linux kernel — upgrade to kernel 3.10.0-693.1.1 or later on RHEL 7/CentOS 7, or kernel 4.13.1+ on other distributions. This is the definitive fix.

2. Migrate from CentOS 7 — CentOS 7 reached end of life June 30, 2024 and no longer receives kernel security patches; migrate to AlmaLinux 8/9, Rocky Linux 8/9, or RHEL 8/9.

3. Workaround (if patching is delayed): Set vm.legacy_va_layout = 1 via sysctl, which changes the virtual address space layout and avoids the overlap condition. This is a temporary mitigation only:

   sysctl -w vm.legacy_va_layout=1
   

4. Restrict local access — limit shell access to servers to the minimum required set of users; CVE-2017-1000253 requires an interactive shell or the ability to execute binaries on the target system.

5. Apply container isolation — containerized workloads sharing a vulnerable host kernel are all exposed; patching the host kernel protects all containers simultaneously.