CVE-2016-4429
Description
From CVE.org
Stack-based buffer overflow in the clntudp_call function in sunrpc/clnt_udp.c in the GNU C Library (aka glibc or libc6) allows remote servers to cause a denial of service (crash) or possibly unspecified other impact via a flood of crafted ICMP and UDP packets.
Statement
Based on technical analysis of this flaw:
On Red Hat Enterprise Linux 6: No looping behaviour was observed. Without the looping behavior, the alloca should be harmless for pretty much all applications because the size argument depends on the size of the generated (outgoing) UDP packet and will be well below default stack sizes. Therefore it is not affected by this flaw.
On Red Hat Enterprise Linux 7: Looping behaviour was observed and segfaults with small stack sizes. -fstack-class-protection will turn this into a reliable crash (no code execution possible). Even without that build flag, this will not be exploitable in most cases because the application determines the alloca argument, based on the generated UDP packet (not the response). This will usually be smaller than a page. The maximum impact is therefore crash, there is no code execution involved.
This issue was fixed in glibc-2.23.1, therefore Red Hat Enterprise Linux 8 is not affected by this flaw.
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).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | 5.9 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v2 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 2.6 | 4.3 | N/A |
| Attack Vector | Network | Network | N/A |
| Access Complexity | High | Medium | N/A |
| Authentication | None | None | N/A |
| Confidentiality Impact | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | Partial | Partial | N/A |
Vector
Red Hat: AV:N/AC:H/Au:N/C:N/I:N/A:P
NVD: AV:N/AC:M/Au:N/C:N/I:N/A:P
Understanding the Weakness (CWE)
Availability
Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
Integrity,Confidentiality,Availability,Access Control
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands; Bypass Protection Mechanism
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy.
Integrity,Confidentiality,Availability,Access Control,Other
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Other
When the consequence is arbitrary code execution, this can often be used to subvert any other security service.
Acknowledgements
This issue was discovered by Aldy Hernandez (Red Hat).
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