In NLnet Labs Unbound up to and including 1.26.0, a vulnerability was found in that can progressively corrupt heap memory and under certain systems and compilation options could lead to remote code execution. The vulnerability starts when CNAME synthesis during an upstream response needs to enforce(rewrite) a max TTL value in the packet buffer. Coupled with a compression pointer that points to the overwritten value and invalidates the domain name, it leads to an error path that does not properly move the buffer position and allows for the heap buffer overflow. Since this is heavily reliant on heap memory layout, results are memory corruption that eventually leads to a crash and under specific systems and compilation options remote code execution.
Weakness
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Unbound | Nlnetlabs | * | 1.26.1 (excluding) |
| Red Hat Enterprise Linux 10 | RedHat | unbound-0:1.24.2-7.el10_2.6 | * |
| Red Hat Enterprise Linux 8 | RedHat | unbound-0:1.16.2-5.14.el8_10.4 | * |
| Red Hat Enterprise Linux 9 | RedHat | unbound-0:1.24.2-3.el9_8.8 | * |
| Red Hat OpenShift Container Platform 4.22 | RedHat | rhcos-4.22.9.8.202609291947-0 | * |
| Red Hat Hardened Images | RedHat | unbound-main-1.26.1-1.hum1 | * |
| Unbound | Ubuntu | esm-infra-legacy/trusty | * |
| Unbound | Ubuntu | esm-infra-legacy/xenial | * |
| Unbound | Ubuntu | esm-infra/bionic | * |
| Unbound | Ubuntu | esm-infra/focal | * |
| Unbound | Ubuntu | jammy | * |
| Unbound | Ubuntu | noble | * |
| Unbound | Ubuntu | resolute | * |
| Unbound | Ubuntu | upstream | * |
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].