Cisco IOS and IOS XE Remote Code Execution
CVE-2017-3881 is a critical-severity improper input validation vulnerability in Cisco IOS and IOS XE Software, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Cisco IOS and IOS XE Software versions: Cisco IOS and IOS XE Software. The record does not name a fixed version, so check the vendor advisory. CISA added it to the Known Exploited Vulnerabilities catalogue on March 25, 2022, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Check which version of Cisco IOS and IOS XE Software you run against the affected versions below, and install the vendor's latest release.
- CISA's required action: Apply updates per vendor instructions.
- Read the advisory on tools.cisco.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Cisco IOS and IOS XE Software | Cisco IOS and IOS XE Software | Cisco IOS and IOS XE Software | Not stated |
| Cisco | iOS | 12.2s through 15.1\(3\)svs | Not stated |
| Cisco | iOS Xe | 3.2sg through 3.9e | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | NVD |
| CVSS 3.1 | 9.8 | Critical | CISA (ADP) |
| CVSS 2.0 | 10.0 | High | NVD |
Official description
A vulnerability in the Cisco Cluster Management Protocol (CMP) processing code in Cisco IOS and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a reload of an affected device or remotely execute code with elevated privileges. The Cluster Management Protocol utilizes Telnet internally as a signaling and command protocol between cluster members. The vulnerability is due to the combination of two factors: (1) the failure to restrict the use of CMP-specific Telnet options only to internal, local communications between cluster members and instead accept and process such options over any Telnet connection to an affected device; and (2) the incorrect processing of malformed CMP-specific Telnet options. An attacker could exploit this vulnerability by sending malformed CMP-specific Telnet options while establishing a Telnet session with an affected Cisco device configured to accept Telnet connections. An exploit could allow an attacker to execute arbitrary code and obtain full control of the device or cause a reload of the affected device. This affects Catalyst switches, Embedded Service 2020 switches, Enhanced Layer 2 EtherSwitch Service Module, Enhanced Layer 2/3 EtherSwitch Service Module, Gigabit Ethernet Switch Module (CGESM) for HP, IE Industrial Ethernet switches, ME 4924-10GE switch, RF Gateway 10, and SM-X Layer 2/3 EtherSwitch Service Module. Cisco Bug IDs: CSCvd48893.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Input Validation
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
How developers prevent this class of flaw
- Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build recognizers for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses.
- Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
- Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- securityfocus.com/bid/96960Third Party Advisory, VDB Entry
- securityfocus.com/bid/97391Third Party Advisory, VDB Entry
- securitytracker.com/id/1038059Third Party Advisory, VDB Entry
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2017-3881US Government Resource
Technical write-ups (may include proof of concept)
- exploit-db.com/exploits/41872/Exploit, Third Party Advisory, VDB Entry
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