CVE-2026-40469 in gawk
Summary
by MITRE • 07/13/2026
Integer overflow vulnerability has been found in "builtin.c" program file of gawk (do_sub() routine). This issue could be used to overwrite gawk heap metadata and objects causing the program to crash. It affects 32-bit builds of gawk in versions 5.4.0 and below.
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Analysis
by VulDB Data Team • 07/13/2026
The integer overflow vulnerability discovered in gawk's builtin.c file within the do_sub() routine represents a critical security flaw that can lead to heap corruption and arbitrary code execution. This vulnerability specifically impacts 32-bit builds of gawk versions 5.4.0 and earlier, making it particularly concerning for systems that rely on legacy architectures or older software versions. The flaw arises from improper handling of integer arithmetic during string substitution operations, where the program fails to properly validate or constrain input values before performing calculations that could exceed the maximum representable value for signed integers.
The technical implementation of this vulnerability stems from a lack of proper bounds checking in the do_sub() function which processes substitution operations within gawk's awk scripting environment. When processing certain malformed inputs that trigger the string replacement logic, the routine performs arithmetic operations on integer variables that can overflow when dealing with large input sizes or complex pattern matching scenarios. This overflow condition results in corrupted heap metadata structures and potentially overwrites adjacent memory objects, creating a scenario where subsequent memory operations may dereference invalid pointers or corrupt program state.
The operational impact of this vulnerability extends beyond simple program crashes to potentially enable more sophisticated attacks depending on the execution environment and memory layout. An attacker who can control the input to gawk's substitution functions could leverage this integer overflow to manipulate heap structures, potentially leading to information disclosure, denial of service, or in some cases, arbitrary code execution if proper memory protections are not in place. The vulnerability is particularly dangerous in environments where gawk is used with untrusted input such as web applications, automated processing systems, or scripting environments that handle user-provided data.
Mitigation strategies for this integer overflow vulnerability should focus on immediate patching of affected gawk versions to the latest releases where the flaw has been addressed through proper integer bounds checking and input validation. System administrators should prioritize updating 32-bit installations of gawk to versions 5.4.1 or later, as these releases contain the necessary fixes for the do_sub() routine's arithmetic operations. Additionally, implementing input sanitization measures at the application level can provide defense-in-depth protection against exploitation attempts. Organizations should also consider disabling unnecessary gawk usage in environments where untrusted input processing occurs, and deploy heap-based memory protection mechanisms such as stack canaries or address space layout randomization to reduce exploitability. This vulnerability aligns with CWE-190 which specifically addresses integer overflow conditions, and could potentially map to ATT&CK technique T1059.007 for scripting languages used in command and control operations.
The root cause analysis reveals that this vulnerability demonstrates poor software engineering practices in handling arithmetic operations within memory-sensitive contexts. The lack of proper integer overflow detection mechanisms during string processing operations indicates a failure to follow secure coding guidelines that emphasize input validation and bounds checking. Modern defensive programming approaches would require explicit checks for integer overflow conditions before performing arithmetic operations, particularly when dealing with user-controlled data that could potentially drive the calculation beyond representable limits. This type of vulnerability serves as an important reminder of why comprehensive testing including fuzzing and static analysis should be part of the software development lifecycle to identify such memory corruption issues before deployment in production environments.