CVE-2018-25032
Description
An out-of-bounds access flaw was found in zlib, which allows memory corruption when deflating (ex: when compressing) if the input has many distant matches. For some rare inputs with a large number of distant matches (crafted payloads), the buffer into which the compressed or deflated data is written can overwrite the distance symbol table which it overlays. This issue results in corrupted output due to invalid distances, which leads to out-of-bound access, corrupting the memory and potentially crashing the application.
Statement
This bug was introduced in zlib v1.2.2.2 through zlib v1.2.11, with the addition of the Z_FIXED option, which forces the use of fixed Huffman codes, rather than dynamic Huffman codes, allowing for a simpler decoder for special applications.
This bug is difficult to trigger, as Z_FIXED is usually only used in special circumstances.
Rsync does the compression in-transit using zlib. As rsync uses vulnerable zlib v1.2.8 package, which incorrectly handles memory when performing certain zlib compressing or deflating operations. This results in rsync to crash.
Note - The issue wasn't publicly labelled as security vulnerability until 2022, but the fix was public since 2018.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.2 | 7.5 | 7.5 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | Low | Low | Low |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | None | None | None |
| Integrity Impact | Low | None | None |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Red Hat CVSS v3 Score Explanation
Red Hat sets I:L, because when there is an input with large number of distant matches (ex: any crafted payload), the buffer into which the compressed or deflated data is written can overwrite the distance symbol table which it overlays. This could probably leads to memory corruption causing harm to Data Integrity. Whereas, highest impact is to availability.
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands; Modify Memory
If the memory accessible by the attacker can be effectively controlled, it may be possible to execute arbitrary code, as with a standard buffer overflow. If the attacker can overwrite a pointer's worth of memory (usually 32 or 64 bits), they can alter the intended control flow by redirecting a function pointer to their own malicious code. Even when the attacker can only modify a single byte arbitrary code execution can be possible. Sometimes this is because the same problem can be exploited repeatedly to the same effect. Other times it is because the attacker can overwrite security-critical application-specific data -- such as a flag indicating whether the user is an administrator.
Availability,Confidentiality
Technical Impact: Read Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
Confidentiality
Technical Impact: Read Memory
In the case of an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffer's position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.
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