CVE-2026-40468 Overview
CVE-2026-40468 is an integer overflow vulnerability [CWE-190] in the builtin.c source file of GNU gawk, the GNU implementation of the AWK text-processing language. The flaw affects gawk versions 5.4.0 and earlier. A local attacker supplying crafted input can trigger memory exhaustion on the host operating system. The same condition can be leveraged to overwrite gawk heap metadata and adjacent heap objects with attacker-controlled bytes. Exploitation requires local access and no privileges, but successful abuse depends on specific runtime conditions.
Critical Impact
An integer overflow in builtin.c allows a local attacker to exhaust host memory and corrupt gawk heap metadata with attacker-controlled bytes, potentially undermining process integrity.
Affected Products
- GNU gawk versions 5.4.0 and below
- Linux and Unix distributions bundling vulnerable gawk builds
- Automation pipelines and scripts that pass untrusted input to gawk
Discovery Timeline
- 2026-07-13 - CVE-2026-40468 published to the National Vulnerability Database
- 2026-07-14 - Last updated in NVD database
Technical Details for CVE-2026-40468
Vulnerability Analysis
The vulnerability resides in builtin.c, the source file that implements built-in functions such as string, array, and I/O helpers in gawk. An arithmetic operation involving a size or length value overflows its integer type. The resulting truncated value is subsequently used as an allocation size or loop bound, producing an undersized allocation followed by an out-of-bounds write, or an unbounded allocation request that exhausts memory.
Because the overflow feeds heap allocation logic, exploitation can corrupt glibc heap metadata and neighboring chunks. This condition falls under the class of integer overflow bugs that lead to heap-based memory corruption, matching the [CWE-190] weakness classification.
Refer to the GNU Gawk commit notification and the CERT PL analysis for the upstream diff and analytical context.
Root Cause
The root cause is missing validation of an integer value before it is used as a size argument in a heap allocation path within builtin.c. When the input length crosses the representable range of the integer type, the wrapped value bypasses subsequent size checks. The allocator then returns a buffer that does not match the caller's assumptions about capacity.
Attack Vector
Exploitation is local. An attacker must be able to run gawk or influence its input, for example by feeding a crafted file, environment value, or script fragment to a process that invokes gawk. Server-side automation, CI/CD jobs, log processors, and shell pipelines that hand untrusted data to gawk widen the attack surface. Remote exploitation is not possible without an intermediary that channels attacker-controlled data into a local gawk invocation.
No verified public proof-of-concept code exists for this issue. See the upstream patch commit 062f2f2581b991362c046f7f2e238ffa34e6f8c7 for the specific code paths modified.
Detection Methods for CVE-2026-40468
Indicators of Compromise
- Unexpected gawk process crashes with SIGSEGV or SIGABRT, particularly with glibc heap corruption messages such as malloc(): corrupted top size or double free or corruption.
- Sudden growth of resident memory for gawk processes leading to OOM-killer events recorded in dmesg or /var/log/messages.
- Automation jobs consuming abnormally large gawk input followed by aborted runs.
Detection Strategies
- Inventory installed gawk versions across Linux hosts using package managers such as rpm -q gawk or dpkg -s gawk and flag any version at or below 5.4.0.
- Alert on gawk invocations with input sourced from world-writable paths, network sockets, or untrusted upload directories.
- Correlate gawk process termination events with kernel OOM-kill entries to surface memory-exhaustion attempts.
Monitoring Recommendations
- Enable audit rules (auditd) on execution of /usr/bin/gawk and related symlinks to capture command-line arguments and parent processes.
- Track cgroup memory usage for job schedulers and CI runners that call gawk to catch runaway allocations early.
- Ship process telemetry and crash artifacts to a central SIEM or data lake for retrospective hunting against the version inventory.
How to Mitigate CVE-2026-40468
Immediate Actions Required
- Upgrade gawk to a fixed release that includes upstream commit 062f2f2581b991362c046f7f2e238ffa34e6f8c7 as soon as vendor packages are available.
- Identify every script, cron job, and pipeline that pipes untrusted input into gawk and restrict those data sources until patching is complete.
- Apply per-process memory limits with ulimit -v or systemd MemoryMax= to contain memory-exhaustion attempts.
Patch Information
The upstream fix is available in the GNU gawk Git repository as commit 062f2f2581b991362c046f7f2e238ffa34e6f8c7. Details are published in the GNU Gawk commit notification. Distribution maintainers will backport the change into 5.4.x and earlier supported branches; consult your Linux vendor's security advisories for package versions.
Workarounds
- Prevent execution of gawk against attacker-controlled input by validating and truncating input sizes at the calling script layer.
- Run gawk inside a sandbox such as bwrap, firejail, or a rootless container with strict memory and file access limits.
- Substitute mawk or busybox awk for non-GNU-specific tasks where feasible, until patched gawk binaries are deployed.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
