CVE Vulnerabilities


Improper Input Validation

Published: Mar 28, 2019 | Modified: Oct 09, 2019
CVSS 3.x
CVSS 2.x
7.8 HIGH

A vulnerability in the Network-Based Application Recognition (NBAR) feature of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload. This vulnerability is due to a parsing issue on DNS packets. An attacker could exploit these vulnerabilities by sending crafted DNS packets through routers that are running an affected version and have NBAR enabled. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a denial of service (DoS) condition.


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.

Affected Software

Name Vendor Start Version End Version
Ios Cisco 15.1(2)sg8a 15.1(2)sg8a
Ios Cisco 15.1(3)svg3d 15.1(3)svg3d
Ios Cisco 15.1(3)svi1b 15.1(3)svi1b
Ios Cisco 15.1(3)svk4b 15.1(3)svk4b
Ios Cisco 15.1(3)svk4c 15.1(3)svk4c
Ios Cisco 15.1(3)svm3 15.1(3)svm3
Ios Cisco 15.1(3)svn2 15.1(3)svn2
Ios Cisco 15.1(3)svo1 15.1(3)svo1
Ios Cisco 15.1(3)svo2 15.1(3)svo2
Ios Cisco 15.1(3)svo3 15.1(3)svo3
Ios Cisco 15.1(3)svo4 15.1(3)svo4
Ios Cisco 15.1(3)svp1 15.1(3)svp1
Ios Cisco 15.1(3)svp2 15.1(3)svp2
Ios Cisco 15.1(4)m12c 15.1(4)m12c
Ios Cisco 15.2(3)ea1 15.2(3)ea1
Ios Cisco 15.2(4a)ea5 15.2(4a)ea5
Ios Cisco 15.3(3)ja1n 15.3(3)ja1n
Ios Cisco 15.3(3)jd 15.3(3)jd
Ios Cisco 15.3(3)jd2 15.3(3)jd2
Ios Cisco 15.3(3)jd3 15.3(3)jd3
Ios Cisco 15.3(3)jd4 15.3(3)jd4
Ios Cisco 15.3(3)jd5 15.3(3)jd5
Ios Cisco 15.3(3)jd6 15.3(3)jd6
Ios Cisco 15.3(3)jd7 15.3(3)jd7
Ios Cisco 15.3(3)jd8 15.3(3)jd8
Ios Cisco 15.3(3)jd9 15.3(3)jd9
Ios Cisco 15.3(3)jd11 15.3(3)jd11
Ios Cisco 15.3(3)jd12 15.3(3)jd12
Ios Cisco 15.3(3)jd13 15.3(3)jd13
Ios Cisco 15.3(3)jd14 15.3(3)jd14
Ios Cisco 15.3(3)je 15.3(3)je
Ios Cisco 15.3(3)jf 15.3(3)jf
Ios Cisco 15.3(3)jf1 15.3(3)jf1
Ios Cisco 15.3(3)jf2 15.3(3)jf2
Ios Cisco 15.3(3)jf4 15.3(3)jf4
Ios Cisco 15.3(3)jf5 15.3(3)jf5
Ios Cisco 15.3(3)jf35 15.3(3)jf35
Ios Cisco 15.3(3)jg 15.3(3)jg
Ios Cisco 15.3(3)jg1 15.3(3)jg1
Ios Cisco 15.3(3)jh 15.3(3)jh
Ios Cisco 15.3(3)ji 15.3(3)ji
Ios Cisco 15.3(3)ji2 15.3(3)ji2
Ios Cisco 15.3(3)jnp 15.3(3)jnp
Ios Cisco 15.3(3)jnp1 15.3(3)jnp1
Ios Cisco 15.3(3)jnp3 15.3(3)jnp3
Ios Cisco 15.3(3)jpb 15.3(3)jpb
Ios Cisco 15.3(3)jpb1 15.3(3)jpb1
Ios Cisco 15.3(3)jpc 15.3(3)jpc
Ios Cisco 15.3(3)jpc1 15.3(3)jpc1
Ios Cisco 15.3(3)jpc2 15.3(3)jpc2
Ios Cisco 15.3(3)jpc3 15.3(3)jpc3
Ios Cisco 15.3(3)jpc5 15.3(3)jpc5
Ios Cisco 15.3(3)jpd 15.3(3)jpd
Ios Cisco 15.5(3)m 15.5(3)m
Ios Cisco 15.5(3)m0a 15.5(3)m0a
Ios Cisco 15.5(3)m1 15.5(3)m1
Ios Cisco 15.5(3)m2 15.5(3)m2
Ios Cisco 15.5(3)m2a 15.5(3)m2a
Ios Cisco 15.5(3)m3 15.5(3)m3
Ios Cisco 15.5(3)m4 15.5(3)m4
Ios Cisco 15.5(3)m4a 15.5(3)m4a
Ios Cisco 15.5(3)m4b 15.5(3)m4b
Ios Cisco 15.5(3)m4c 15.5(3)m4c
Ios Cisco 15.5(3)m5 15.5(3)m5
Ios Cisco 15.5(3)m5a 15.5(3)m5a
Ios Cisco 15.5(3)s 15.5(3)s
Ios Cisco 15.5(3)s0a 15.5(3)s0a
Ios Cisco 15.5(3)s1 15.5(3)s1
Ios Cisco 15.5(3)s1a 15.5(3)s1a
Ios Cisco 15.5(3)s2 15.5(3)s2
Ios Cisco 15.5(3)s3 15.5(3)s3
Ios Cisco 15.5(3)s4 15.5(3)s4
Ios Cisco 15.5(3)s5 15.5(3)s5
Ios Cisco 15.5(3)sn 15.5(3)sn
Ios Cisco 15.5(3)sn0a 15.5(3)sn0a
Ios Cisco 15.6(1)s 15.6(1)s
Ios Cisco 15.6(1)s1 15.6(1)s1
Ios Cisco 15.6(1)s2 15.6(1)s2
Ios Cisco 15.6(1)s3 15.6(1)s3
Ios Cisco 15.6(1)s4 15.6(1)s4
Ios Cisco 15.6(1)sn 15.6(1)sn
Ios Cisco 15.6(1)sn1 15.6(1)sn1
Ios Cisco 15.6(1)sn2 15.6(1)sn2
Ios Cisco 15.6(1)sn3 15.6(1)sn3
Ios Cisco 15.6(1)t 15.6(1)t
Ios Cisco 15.6(1)t0a 15.6(1)t0a
Ios Cisco 15.6(1)t1 15.6(1)t1
Ios Cisco 15.6(1)t2 15.6(1)t2
Ios Cisco 15.6(2)s 15.6(2)s
Ios Cisco 15.6(2)s1 15.6(2)s1
Ios Cisco 15.6(2)s2 15.6(2)s2
Ios Cisco 15.6(2)s3 15.6(2)s3
Ios Cisco 15.6(2)s4 15.6(2)s4
Ios Cisco 15.6(2)sn 15.6(2)sn
Ios Cisco 15.6(2)sp3b 15.6(2)sp3b
Ios Cisco 15.6(2)t 15.6(2)t
Ios Cisco 15.6(2)t0a 15.6(2)t0a
Ios Cisco 15.6(2)t1 15.6(2)t1
Ios Cisco 15.6(2)t2 15.6(2)t2
Ios Cisco 15.6(3)m 15.6(3)m
Ios Cisco 15.6(3)m0a 15.6(3)m0a
Ios Cisco 15.6(3)m1 15.6(3)m1
Ios Cisco 15.6(3)m1a 15.6(3)m1a
Ios Cisco 15.6(3)m1b 15.6(3)m1b
Ios Cisco 15.6(3)sn 15.6(3)sn
Ios Cisco 15.6(4)sn 15.6(4)sn
Ios Cisco 15.6(5)sn 15.6(5)sn
Ios Cisco 15.6(6)sn 15.6(6)sn
Ios Cisco 15.6(7)sn 15.6(7)sn
Ios_xe Cisco * *
Ios_xe Cisco 3.2.0ja 3.2.0ja
Ios_xe Cisco 3.16.0as 3.16.0as
Ios_xe Cisco 3.16.0bs 3.16.0bs
Ios_xe Cisco 3.16.0cs 3.16.0cs
Ios_xe Cisco 3.16.0s 3.16.0s
Ios_xe Cisco 3.16.1as 3.16.1as
Ios_xe Cisco 3.16.1s 3.16.1s
Ios_xe Cisco 3.16.2as 3.16.2as
Ios_xe Cisco 3.16.2bs 3.16.2bs
Ios_xe Cisco 3.16.2s 3.16.2s
Ios_xe Cisco 3.16.3as 3.16.3as
Ios_xe Cisco 3.16.3s 3.16.3s
Ios_xe Cisco 3.16.4as 3.16.4as
Ios_xe Cisco 3.16.4bs 3.16.4bs
Ios_xe Cisco 3.16.4cs 3.16.4cs
Ios_xe Cisco 3.16.4ds 3.16.4ds
Ios_xe Cisco 3.16.4es 3.16.4es
Ios_xe Cisco 3.16.4gs 3.16.4gs
Ios_xe Cisco 3.16.4s 3.16.4s
Ios_xe Cisco 3.16.5as 3.16.5as
Ios_xe Cisco 3.16.5s 3.16.5s
Ios_xe Cisco 3.17.0s 3.17.0s
Ios_xe Cisco 3.17.1as 3.17.1as
Ios_xe Cisco 3.17.1s 3.17.1s
Ios_xe Cisco 3.17.3s 3.17.3s
Ios_xe Cisco 3.17.4s 3.17.4s
Ios_xe Cisco 3.18.0as 3.18.0as
Ios_xe Cisco 3.18.0s 3.18.0s
Ios_xe Cisco 3.18.0sp 3.18.0sp
Ios_xe Cisco 3.18.1asp 3.18.1asp
Ios_xe Cisco 3.18.1bsp 3.18.1bsp
Ios_xe Cisco 3.18.1csp 3.18.1csp
Ios_xe Cisco 3.18.1gsp 3.18.1gsp
Ios_xe Cisco 3.18.1hsp 3.18.1hsp
Ios_xe Cisco 3.18.1isp 3.18.1isp
Ios_xe Cisco 3.18.1s 3.18.1s
Ios_xe Cisco 3.18.1sp 3.18.1sp
Ios_xe Cisco 3.18.2asp 3.18.2asp
Ios_xe Cisco 3.18.2s 3.18.2s
Ios_xe Cisco 3.18.2sp 3.18.2sp
Ios_xe Cisco 3.18.3s 3.18.3s
Ios_xe Cisco 3.18.4s 3.18.4s
Ios_xe Cisco 16.2.1 16.2.1
Ios_xe Cisco 16.2.2 16.2.2
Ios_xe Cisco 16.3.1 16.3.1
Ios_xe Cisco 16.3.1a 16.3.1a
Ios_xe Cisco 16.3.2 16.3.2
Ios_xe Cisco 16.3.3 16.3.3
Ios_xe Cisco 16.3.4 16.3.4
Ios_xe Cisco 16.4.1 16.4.1
Ios_xe Cisco 16.4.2 16.4.2
Ios_xe Cisco 16.4.3 16.4.3
Ios_xe Cisco 16.5.1 16.5.1
Ios_xe Cisco 16.5.1a 16.5.1a
Ios_xe Cisco 16.5.1b 16.5.1b

Extended Description

Input validation is a frequently-used technique for checking potentially dangerous inputs in order to ensure that the inputs are safe for processing within the code, or when communicating with other components. When software does not validate input properly, an attacker is able to craft the input in a form that is not expected by the rest of the application. This will lead to parts of the system receiving unintended input, which may result in altered control flow, arbitrary control of a resource, or arbitrary code execution. Input validation is not the only technique for processing input, however. Other techniques attempt to transform potentially-dangerous input into something safe, such as filtering (CWE-790) - which attempts to remove dangerous inputs - or encoding/escaping (CWE-116), which attempts to ensure that the input is not misinterpreted when it is included in output to another component. Other techniques exist as well (see CWE-138 for more examples.) Input validation can be applied to:

Data can be simple or structured. Structured data can be composed of many nested layers, composed of combinations of metadata and raw data, with other simple or structured data. Many properties of raw data or metadata may need to be validated upon entry into the code, such as:

Implied or derived properties of data must often be calculated or inferred by the code itself. Errors in deriving properties may be considered a contributing factor to improper input validation.

Note that “input validation” has very different meanings to different people, or within different classification schemes. Caution must be used when referencing this CWE entry or mapping to it. For example, some weaknesses might involve inadvertently giving control to an attacker over an input when they should not be able to provide an input at all, but sometimes this is referred to as input validation. Finally, it is important to emphasize that the distinctions between input validation and output escaping are often blurred, and developers must be careful to understand the difference, including how input validation is not always sufficient to prevent vulnerabilities, especially when less stringent data types must be supported, such as free-form text. Consider a SQL injection scenario in which a person’s last name is inserted into a query. The name “O’Reilly” would likely pass the validation step since it is a common last name in the English language. However, this valid name cannot be directly inserted into the database because it contains the “'” apostrophe character, which would need to be escaped or otherwise transformed. In this case, removing the apostrophe might reduce the risk of SQL injection, but it would produce incorrect behavior because the wrong name would be recorded.

Potential Mitigations

  • Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
  • When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
  • Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
  • For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
  • Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.
  • Inputs should be decoded and canonicalized to the application’s current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control.
  • Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.