Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
CWE-377 Class Incomplete
Insecure Temporary File
This vulnerability occurs when an application creates temporary files with insecure permissions or in predictable locations, allowing attackers to read, modify, or delete sensitive data.
Definition
What is CWE-377?
This vulnerability occurs when an application creates temporary files with insecure permissions or in predictable locations, allowing attackers to read, modify, or delete sensitive data.
Insecure temporary files are a common but dangerous flaw. They happen when developers use predictable filenames, place files in world-writable directories, or set overly permissive file access rights. Attackers can exploit this by 'symlinking' a predictable filename to a critical system file, performing a race condition to replace the file after creation, or simply reading the exposed data. This can lead to information disclosure, data corruption, or even a full system compromise.
Preventing this requires using secure, random filenames, setting restrictive file permissions (like 0600), and leveraging secure system APIs designed for temporary file creation. Managing this at scale across numerous applications is difficult; an ASPM like Plexicus can help you track and remediate these flaws across your entire stack. While SAST tools catch the pattern, Plexicus uses AI to suggest the actual code fix, such as replacing insecure `tmpnam()` calls with secure `mkstemp()`, saving hours of manual work.
Real-world impact
Real-world CVEs caused by CWE-377
-
A library uses the Java File.createTempFile() method which creates a file with "-rw-r--r--" default permissions on Unix-like operating systems
How attackers exploit it
Step-by-step attacker path
- 1
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 4
Iterate until the response leaks data, executes attacker code, or escalates privileges.
Vulnerable code example
Vulnerable C
The following code uses a temporary file for storing intermediate data gathered from the network before it is processed.
if (tmpnam_r(filename)) {
FILE* tmp = fopen(filename,"wb+");
while((recv(sock,recvbuf,DATA_SIZE, 0) > 0)&(amt!=0)) amt = fwrite(recvbuf,1,DATA_SIZE,tmp);
}
... Secure code example
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-377
- Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
- Implementation Validate input at trust boundaries; use allowlists, not denylists.
- Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
- Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
- Operation Monitor logs for the runtime signals listed in the next section.
Detection signals
How to detect CWE-377
Plexicus auto-detects CWE-377 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-377?
How serious is CWE-377?
What languages or platforms are affected by CWE-377?
How can I prevent CWE-377?
How does Plexicus detect and fix CWE-377?
Where can I learn more about CWE-377?
Frequently asked questions
What is CWE-377?
This vulnerability occurs when an application creates temporary files with insecure permissions or in predictable locations, allowing attackers to read, modify, or delete sensitive data.
How serious is CWE-377?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-377?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-377?
Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.
How does Plexicus detect and fix CWE-377?
Plexicus's SAST engine matches the data-flow signature for CWE-377 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-377?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/377.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-377
CWE-668 Parent
Exposure of Resource to Wrong Sphere
This vulnerability occurs when an application unintentionally makes a resource accessible to users or systems that should not have…
CWE-1189 Sibling
Improper Isolation of Shared Resources on System-on-a-Chip (SoC)
This vulnerability occurs when a System-on-a-Chip (SoC) fails to properly separate shared hardware resources between secure (trusted) and…
CWE-1282 Sibling
Assumed-Immutable Data is Stored in Writable Memory
This vulnerability occurs when data that should be permanent and unchangeable—like a bootloader, device IDs, or one-time configuration…
CWE-1327 Sibling
Binding to an Unrestricted IP Address
This vulnerability occurs when software or a service is configured to bind to the IP address 0.0.0.0 (or :: in IPv6), which acts as a…
CWE-1331 Sibling
Improper Isolation of Shared Resources in Network On Chip (NoC)
This vulnerability occurs when a Network on Chip (NoC) fails to properly separate its internal, shared resources—like buffers, switches,…
CWE-134 Sibling
Use of Externally-Controlled Format String
This vulnerability occurs when a program uses a format string from an untrusted, external source (like user input, a network packet, or a…
CWE-200 Sibling
Exposure of Sensitive Information to an Unauthorized Actor
This weakness occurs when an application unintentionally reveals sensitive data to someone who shouldn't have access to it.
CWE-374 Sibling
Passing Mutable Objects to an Untrusted Method
This vulnerability occurs when a function receives a direct reference to mutable data, such as an object or array, instead of a safe copy…
CWE-375 Sibling
Returning a Mutable Object to an Untrusted Caller
This vulnerability occurs when a method directly returns a reference to its internal mutable data, allowing untrusted calling code to…
Resources
Further reading
- MITRE — official CWE-377 https://cwe.mitre.org/data/definitions/377.html
- Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf
- Writing Secure Code https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223
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