Synonym for "Blind Spot"

Solution 1:

Since you're asking for a computing term, I suggest "vulnerability". From a security point of view, this is the main concern.

Vulnerability — Wikipedia

In computer security, a vulnerability is a weakness which allows an attacker to reduce a system's information assurance. Vulnerability is the intersection of three elements: a system susceptibility or flaw, attacker access to the flaw, and attacker capability to exploit the flaw.

To exploit a vulnerability, an attacker must have at least one applicable tool or technique that can connect to a system weakness. In this frame, vulnerability is also known as the attack surface.

Or software bug — Wikipedia

A software bug is an error, flaw, failure or fault in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways.

Most bugs arise from mistakes and errors made by people in either a program's source code or its design, or in frameworks and operating systems used by such programs, and a few are caused by compilers producing incorrect code.

A program that contains a large number of bugs, and/or bugs that seriously interfere with its functionality, is said to be buggy or defective. Reports detailing bugs in a program are commonly known as bug reports, defect reports, fault reports, problem reports, trouble reports, change requests and so forth.

Or glitch — Wikipedia, if it's a short-term issue.

A glitch is a short-lived fault in a system. It is often used to describe a transient fault that corrects itself, and is therefore difficult to troubleshoot. The term is particularly common in the computing and electronics industries, and in circuit bending, as well as among players of video games, although it is applied to all types of systems including human organizations and nature.

Solution 2:

Lacuna — OED

noun (plural lacunae /ləˈkjuːniː/ or lacunas)
1 An unfilled space; a gap:

'the journal has filled a lacuna in Middle Eastern studies'

'Thus, divergent growth apparently prompted offsetting, in order for the coral to maintain the lacuna and occupy the space around it.'

'Fill the lacunae in your inspiration by tidily copying out what you have already written.'

Solution 3:

It is hard to guess what do you mean by "weakness". If you mean performance, then the "weakest" part of your program is called [the] bottleneck:

A point of congestion or blockage, in particular.

Solution 4:

In a computer program a point of weakness in a very broad sense could be described as a vulnerability as already mentioned in @NVZ's answer.

In the information security field such a weakness is typically referred to as an attack vector when it is abused as part of an exploit:

a weakness or oversight by which someone of suitable skill and means can gain access to a software or hardware system in order to deliver a payload or achieve a malicious outcome. Attack vectors enable hackers to exploit system vulnerabilities, including the human element through social engineering.

The sum of all such weaknesses exposed in a single system are collectively referred to as the attack surface:

is the sum of the different points (the "attack vectors") where an unauthorized user (the "attacker") can try to enter data to or extract data from an environment.

Solution 5:

“Weak link in the chain”

might do if you consider a computer program a chain of instructions and you are pointing out a specific point of weakness.

…but I wonder whether your efforts would be better spent finding a precise form of words to the weakness in plain and/or technical English.