CVE-2016-1000253: 
PHP vulnerability analysis and mitigation

CVE-2017-1000253 is a Linux kernel vulnerability affecting Position-Independent Executable (PIE) stack buffer handling. The vulnerability was discovered in the Linux kernel's loadelfbinary() function and was initially fixed in April 2015 but not recognized as a security threat at that time. The issue affects Linux distributions that had not patched their long-term kernels with the fix from kernel.org (NVD).

The vulnerability occurs when CONFIGARCHBINFMTELFRANDOMIZEPIE is enabled and using a normal top-down address allocation strategy. The loadelfbinary() function attempts to map a PIE binary into an address range immediately below mm->mmapbase but fails to account for the entire binary size. This results in the first PTLOAD segment being mapped below mm->mmapbase, while subsequent PTLOAD segments are incorrectly mapped above mm->mmapbase into the intended 'gap' between the stack and binary. The vulnerability has received a CVSS v3.1 Base Score of 7.8 (High) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (NVD).

The vulnerability can lead to local privilege escalation, potentially allowing attackers to gain unauthorized access to system resources. The high CVSS score indicates that successful exploitation could result in complete compromise of system confidentiality, integrity, and availability (NVD).

The vulnerability was fixed in April 2015 by commit a87938b2e246b81b4fb713edb371a9fa3c5c3c86 and was backported to Linux 3.10.77 in May 2015. Organizations are advised to apply vendor-provided patches or discontinue use of the product if mitigations are unavailable. CISA requires Federal Civilian Executive Branch (FCEB) agencies to remediate this vulnerability by September 30, 2024 (CISA Alert).