VulnerabilityPublished 16 Sep 2026

CVE-2026-18212: Red Hat build of Keycloak 26.4 · Memory Leak

Affects Red Hat build of Keycloak 26.4Source CVE Database V5

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Not known to be exploited · CVSS 7.5 High.

Data as of 31 Oct 2026, 20:20 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.7% chance of exploitation in 30 days – higher than 53% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
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: None: There is no loss of confidentiality within 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 16 Sep 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 31 Oct 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.

What to do

Affected software

Product	Affected	Fixed in
Red HatRed Hat build of Keycloak 26.4	Affected–	Fixed in–
Red HatRed Hat build of Keycloak 26.4	Affected–	Fixed in–
Red HatRed Hat build of Keycloak 26.4.16	Affected–	Fixed in–
Red HatRed Hat build of Keycloak 26.6	Affected–	Fixed in–
Red HatRed Hat build of Keycloak 26.6	Affected–	Fixed in–
Red HatRed Hat build of Keycloak 26.6.7	Affected–	Fixed in–

AI-suggested

Red Hat currently states that no mitigation is available or that existing options do not meet their criteria for ease of use, deployment, applicability, or stability. Users should monitor the Red Hat advisory for updates on fixes or mitigations. Until a fix is released, risk remains for denial of service via malformed SAML requests.

Description

A flaw was found in the SAML Redirect Binding implementation of Keycloak, an open-source identity and access management solution. The issue occurs because the custom DEFLATE compression and decompression helpers fail to release native zlib memory after use. An unauthenticated attacker can exploit this by sending repeated malformed SAML requests, leading to native memory exhaustion and a denial of service.

Impact

Successful exploitation results in a denial of service condition by exhausting native memory of the Keycloak process, causing it to crash, hang, or become unstable. There is no impact on confidentiality or integrity. The vulnerability can be triggered remotely without authentication.

Summary

This vulnerability in Red Hat Build of Keycloak arises from a memory leak in the SAML Redirect Binding's DEFLATE compression and decompression helpers, which do not release native zlib memory after use. An attacker without authentication can repeatedly send malformed SAML requests to exhaust native memory, causing a denial of service by crashing or hanging the Keycloak process. The root cause is the failure to explicitly release native zlib resources in the SAML DEFLATE helper classes. Red Hat has published an advisory confirming the issue and its impact but currently does not provide a patch or mitigation that meets their standards.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 16 Sep 2026, 15:16 UTC

Technical details

References

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