VulnerabilityPublished 16 Mar 2026

CVE-2026-4240: Open5GS · Denial of Service

Affects Open5GSSource CVE Database V5

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Public exploit available · CVSS 6.9 Medium.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 4.0 base score

6.9Medium

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

EPSS: 0.5% chance of exploitation in 30 days – higher than 46% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 16 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CVSS exploit maturity: proof of concept public
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), CVSS vector, the Metasploit, Exploit-DB and nuclei-templates index as of 29 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
Open5GS	Affected 2.7.0 – 2.7.6 7 affected builds	Fixed in–
GitHubopen5gs/open5gs`pkg:github/open5gs/open5gs`Other threats	Affected 2.7.0 – 2.7.6 7 affected builds	Fixed in–

CPE configurations (1)

cpe:2.3:a:open5gs:open5gs:*:*:*:*:*:*:*:*

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AI-suggested

The definitive mitigation is to upgrade Open5GS to version 2.7.7 or later, where the vulnerability has been patched. Network operators should prioritize this upgrade in their maintenance cycles. In addition, organizations should implement network-level protections such as filtering and rate limiting of CCA-related traffic to reduce exposure to malformed or malicious packets targeting the affected functions. Deploying intrusion detection systems (IDS) with signatures tuned to detect anomalous CCA messages can provide early warning of exploitation attempts. Operators should also isolate the Open5GS SMF component within secure network segments and restrict access to trusted management networks to minimize attack surface. Regularly monitoring system logs and performance metrics can help detect early signs of denial of service conditions. Finally, maintaining an up-to-date inventory of Open5GS deployments and applying security patches promptly is critical to reducing risk.

Description

A vulnerability was determined in Open5GS up to 2.7.6. The affected element is the function smf_gx_cca_cb/smf_gy_cca_cb/smf_s6b_aaa_cb/smf_s6b_sta_cb of the component CCA Handler. This manipulation causes denial of service. The attack can be initiated remotely. The exploit has been publicly disclosed and may be utilized. Upgrading to version 2.7.7 is sufficient to fix this issue. Patch name: 80eb484a6ab32968e755e628b70d1a9c64f012ec. Upgrading the affected component is recommended.

Impact

The primary impact of CVE-2026-4240 is denial of service against the Open5GS SMF component, which is critical for managing session and policy control in 5G networks. Disruption of the SMF can lead to dropped sessions, interrupted subscriber services, and degraded network performance. For mobile network operators and enterprises relying on Open5GS for 5G core infrastructure, this can translate into service outages affecting end users, loss of revenue, and reputational damage. Additionally, denial of service in core network components can complicate incident response and recovery efforts. Given the remote and unauthenticated nature of the exploit, attackers could launch DoS attacks from external networks, increasing the risk of widespread disruption. The vulnerability does not appear to allow data leakage or privilege escalation, limiting its impact to availability. However, in critical telecommunications infrastructure, availability disruptions can have cascading effects on emergency services, IoT deployments, and business continuity.

Summary

CVE-2026-4240 identifies a denial of service vulnerability in Open5GS, an open-source 5G core network implementation widely used for mobile network infrastructure. The vulnerability resides in the CCA Handler component, specifically within the callback functions smf_gx_cca_cb, smf_gy_cca_cb, smf_s6b_aaa_cb, and smf_s6b_sta_cb. These functions handle Credit Control Answer (CCA) messages related to policy and charging control in the 5G core. Improper handling or manipulation of these callbacks can cause the Open5GS SMF (Session Management Function) to crash or become unresponsive, resulting in denial of service. The attack can be launched remotely over the network without requiring authentication or user interaction, making it accessible to unauthenticated attackers. The vulnerability affects Open5GS versions 2.7.0 through 2.7.6. The vendor addressed the issue in version 2.7.7 by correcting the handling logic in the affected functions. The CVSS 4.0 vector (AV:N/AC:L/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P) indicates a network-based attack with low complexity, no privileges or user interaction needed, and limited impact on availability. Although no public exploit code is currently known to be in widespread use, the vulnerability's public disclosure and ease of exploitation make it a credible threat to 5G network operators using Open5GS.

References

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