CVE-2026-121996VulnerabilityPublished 5 Nov 2026

gdbserver's agent-expression parser · Length Validation Flaw

Source GCVE Database

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Authoritative record:CVE-2026-121996· High 8.2

Not known to be exploited · CVSS 8.2 High.

Data as of 5 Nov 2026, 19:35 UTC

CVSS 3.1 base score

8.2High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (redhat)	CVSS 3.1	8.2

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 5 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-px57-gjvm-vwfx

What to do

Affected software

Product	Affected	Fixed in
Red Hat Enterprise Linux 10crash	Affected–	Fixed in–
Red Hat Enterprise Linux 10gdb	Affected–	Fixed in–
Red Hat Enterprise Linux 6gdb	Affected–	Fixed in–
Red Hat Enterprise Linux 7gdb	Affected–	Fixed in–
Red Hat Enterprise Linux 8crash	Affected–	Fixed in–
Red Hat Enterprise Linux 8gcc-toolset-14-gdb	Affected–	Fixed in–

AI-suggested

There is currently no mitigation or patch available for this vulnerability. Since gdbserver lacks an authentication mechanism, the only effective mitigation is to restrict network access to the gdbserver port to trusted users and networks only. Avoid exposing gdbserver to untrusted networks. Monitor Red Hat advisories for any future updates or fixes.

Description

A length validation flaw in gdbserver's agent-expression parser allows an unauthenticated remote attacker with network access to an exposed gdbserver port to read uninitialized heap memory and cause a denial of service. The disclosed heap content includes addresses that can aid in defeating ASLR, potentially facilitating further exploitation. This vulnerability affects gdbserver as shipped with Red Hat Enterprise Linux. There is no authentication in gdbserver, and no mitigation exists other than limiting network exposure.

Impact

The vulnerability allows an unauthenticated remote attacker to read uninitialized heap memory from the gdbserver process, potentially leaking sensitive information such as memory addresses that can defeat ASLR. Additionally, the attacker can cause a denial of service by crashing the gdbserver process. This impacts confidentiality (low) and availability (high) of the affected system. There is no integrity impact. The flaw can be exploited remotely over the network without any authentication or user interaction.

Summary

CVE-2026-121996 is a vulnerability in gdbserver's agent-expression parser caused by improper length validation. An unauthenticated remote attacker can exploit this flaw by sending crafted requests to an exposed gdbserver port, leading to disclosure of uninitialized heap memory and a denial of service via process crash. The leaked heap memory includes addresses useful for bypassing ASLR protections. The flaw is present in gdbserver as distributed with Red Hat Enterprise Linux. The vulnerability has a CVSS v3.1 base score of 8.2 (high severity) with network attack vector, low complexity, no privileges required, no user interaction, unchanged scope, low confidentiality impact (heap memory disclosure), no integrity impact, and high availability impact (crash).

CWE-822Untrusted Pointer Dereference (opens in a new tab)
Base weakness
The product obtains a value from an untrusted source, converts this value to a pointer, and dereferences the resulting pointer.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
Pointer Manipulation (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 5 Nov 2026, 19:35 UTC

WeaknessesCWE-822

Technical details

References

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