CVE-2026-121995 in Red Hat
Summary
by MITRE • 11/05/2026
A stack buffer overflow in the GDB client's tracepoint upload handler allows an attacker-controlled debug stub to corrupt stack memory automatically during connection setup. The overflow results from GDB reading beyond the current reply boundary into a stale prior reply in the shared packet buffer.
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Analysis
by VulDB Data Team • 11/05/2026
The vulnerability identified as CVE-2024-39578 represents a critical security flaw within the GNU Debugger, specifically affecting its client-side tracepoint upload handler. This component is responsible for managing communication between GDB and remote debug stubs during debugging sessions that involve tracing execution flow. The core technical issue stems from improper boundary checking when processing incoming data packets. When GDB receives responses from a debug stub, it utilizes a shared packet buffer to store these replies. However, the implementation fails to strictly validate the length of the current reply against the allocated buffer space before proceeding with subsequent operations. This oversight allows an attacker who controls or can manipulate the behavior of the remote debug stub to craft maliciously sized packets that exceed expected limits.
During the connection setup phase for tracepoint uploads, GDB attempts to read data from this shared packet buffer. Due to the lack of rigorous bounds checking, the software reads beyond the end of the current valid reply boundary and accesses memory associated with a stale prior reply still residing in the same buffer. This action constitutes a classic stack-based buffer overflow, as described by Common Weakness Enumeration identifier CWE-121: Stack Buffer Overflow. The act of reading into this out-of-bounds memory location can lead to the corruption of adjacent stack variables and control data structures. While the immediate description highlights a read operation, such boundary violations often pave the way for more severe exploitation vectors if combined with subsequent write operations or specific execution contexts that allow code injection or arbitrary code execution through return address overwrites.
The operational impact of this vulnerability is significant because it requires an attacker to have control over the debug stub connected to GDB. In typical development environments, developers may connect to custom hardware emulators, proprietary debugging interfaces, or untrusted remote targets for testing purposes. If a malicious actor can position themselves as the target debug interface, they can exploit this flaw during the initial handshake and tracepoint configuration phases. The automatic nature of the corruption means that no additional user interaction is required after the connection is established; the overflow occurs automatically as part of GDB's normal protocol handling logic. This lowers the barrier for exploitation compared to vulnerabilities requiring specific trigger conditions or complex state manipulation beyond simple packet reception.
From a threat modeling perspective, this vulnerability aligns with MITRE ATT&CK technique T1059 Command and Scripting Interpreter if it leads to remote code execution on the developer's machine, allowing an attacker to gain unauthorized access to sensitive source code, credentials stored in environment variables, or other development artifacts. It also relates to CWE-20 Improper Input Validation, as the root cause is the failure to properly sanitize and validate input data received from a potentially untrusted external source. The shared buffer architecture used by GDB for efficiency introduces this risk when boundary checks are not meticulously enforced on every packet read operation.
Mitigation strategies must focus on both immediate patching and long-term architectural improvements. Users of affected versions of GNU Debugger should upgrade to the latest stable release where this issue has been resolved, ensuring that proper bounds checking is implemented in the tracepoint upload handler. Developers integrating GDB into automated pipelines or CI/CD systems should ensure their toolchains are up-to-date to prevent exploitation via scripted debugging sessions. Furthermore, security-conscious development practices recommend adopting static analysis tools configured to detect buffer overflow patterns and enforcing strict input validation protocols for all network-facing components of debuggers. Enabling Address Sanitizer during the building of GDB from source can also help identify similar boundary violations in future updates before they reach production environments.