CVE-2018-14633

A security flaw was found in the chap_server_compute_md5() function in the ISCSI target code in the Linux kernel in a way an authentication request from an ISCSI initiator is processed. An unauthenticated remote attacker can cause a stack buffer overflow and smash up to 17 bytes of the stack. The attack requires the iSCSI target to be enabled on the victim host. Depending on how the targets code was built (i.e. depending on a compiler, compile flags and hardware architecture) an attack may lead to a system crash and thus to a denial-of-service or possibly to a non-authorized access to data exported by an iSCSI target. Due to the nature of the flaw, privilege escalation cannot be fully ruled out, although we believe it is highly unlikely. Kernel versions 4.18.x, 4.14.x and 3.10.x are believed to be vulnerable.

Weakness

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

Affected Software

Potential Mitigations

• Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.
• D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
• Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.
• Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.
• For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

References

• http://www.securityfocus.com/bid/105388
• https://access.redhat.com/errata/RHSA-2018:3651
• https://access.redhat.com/errata/RHSA-2018:3666
• https://access.redhat.com/errata/RHSA-2019:1946
• https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2018-14633
• https://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git/commit/?h=4.19/scsi-fixes\u0026id=1816494330a83f2a064499d8ed2797045641f92c
• https://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git/commit/?h=4.19/scsi-fixes\u0026id=8c39e2699f8acb2e29782a834e56306da24937fe
• https://lists.debian.org/debian-lts-announce/2018/10/msg00003.html
• https://seclists.org/oss-sec/2018/q3/270
• https://usn.ubuntu.com/3775-1/
• https://usn.ubuntu.com/3775-2/
• https://usn.ubuntu.com/3776-1/
• https://usn.ubuntu.com/3776-2/
• https://usn.ubuntu.com/3777-1/
• https://usn.ubuntu.com/3777-2/
• https://usn.ubuntu.com/3777-3/
• https://usn.ubuntu.com/3779-1/
• https://www.debian.org/security/2018/dsa-4308