CVE-2019-3855

An integer overflow flaw which could lead to an out of bounds write was discovered in libssh2 before 1.8.1 in the way packets are read from the server. A remote attacker who compromises a SSH server may be able to execute code on the client system when a user connects to the server.

Weakness

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.

Affected Software

Name	Vendor	Start Version	End Version
Libssh2	Libssh2	*	1.8.1 (excluding)
Red Hat Enterprise Linux 6	RedHat	libssh2-0:1.4.2-3.el6_10.1	*
Red Hat Enterprise Linux 7	RedHat	libssh2-0:1.4.3-12.el7_6.2	*
Red Hat Enterprise Linux 7.3 Advanced Update Support	RedHat	libssh2-0:1.4.3-11.el7_3.1	*
Red Hat Enterprise Linux 7.3 Telco Extended Update Support	RedHat	libssh2-0:1.4.3-11.el7_3.1	*
Red Hat Enterprise Linux 7.3 Update Services for SAP Solutions	RedHat	libssh2-0:1.4.3-11.el7_3.1	*
Red Hat Enterprise Linux 7.4 Extended Update Support	RedHat	libssh2-0:1.4.3-11.el7_4.1	*
Red Hat Enterprise Linux 7.5 Extended Update Support	RedHat	libssh2-0:1.4.3-11.el7_5.1	*
Red Hat Enterprise Linux 8	RedHat	virt:rhel-8000020190510171727.55190bc5	*
Libssh2	Ubuntu	bionic	*
Libssh2	Ubuntu	cosmic	*
Libssh2	Ubuntu	esm-apps/bionic	*
Libssh2	Ubuntu	esm-apps/xenial	*
Libssh2	Ubuntu	esm-infra-legacy/trusty	*
Libssh2	Ubuntu	trusty	*
Libssh2	Ubuntu	trusty/esm	*
Libssh2	Ubuntu	xenial	*

Potential Mitigations

Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
If possible, choose a language or compiler that performs automatic bounds checking.
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
Use libraries or frameworks that make it easier to handle numbers without unexpected consequences.
Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]
Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
Use unsigned integers where possible. This makes it easier to perform validation for integer overflows. When signed integers are required, ensure that the range check includes minimum values as well as maximum values.
Understand the programming language’s underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, “not-a-number” calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-7]
Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.

https://cwe.mitre.org/data/definitions/92.html

NVD	https://nvd.nist.gov/vuln/detail/CVE-2019-3855
CWE	https://cwe.mitre.org/data/definitions/190.html

Integer Overflow or Wraparound

Weakness

Affected Software

Potential Mitigations

References

CVE-2019-3855

Integer Overflow or Wraparound

Weakness

Affected Software

Potential Mitigations

Related Attack Patterns

References