GNU Screen MScrollV Function Denial of Service Vulnerability [CVE-2015-6806]

CVE Number – CVE-2015-6806

A vulnerability in the MScrollV function of GNU Screen could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on a targeted system.

The vulnerability exists because the MScrollV function, as defined in the ansi.c source code file of the affected software, does not properly limit recursion. An attacker could exploit this vulnerability by sending a request that submits malicious input to the targeted system. A successful exploit could trigger a stack overflow condition, resulting in a DoS condition.Proof-of-concept (PoC) code that demonstrates an exploit of this vulnerability is publicly available. GNU has confirmed the vulnerability and released software updates.

Analysis

• To exploit this vulnerability, an attacker must send a request that submits malicious input to the targeted system, making exploitation more difficult in environments that restrict network access from untrusted sources.

Safeguards

• Administrators are advised to apply the appropriate updates.
  
  Administrators are advised to allow only trusted users to have network access.
  
  Administrators are advised to run both firewall and antivirus applications to minimize the potential of inbound and outbound threats.
  
  Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.
  
  Administrators can help protect affected systems from external attacks by using a solid firewall strategy.
  
  Administrators are advised to monitor affected systems.

Vendor Announcements

• GNU has released a bug report at the following link: Bug #45713

Fixed Software

• GNU has released software updates at the following link: Fix stack overflow due to too deep recursion