CVE-2025-20335VulnerabilityPublished 3 Sep 2025

CVE-2025-20335: Cisco Session Initiation Protocol (SIP) Software · Improper Access Control

Affects Cisco Session Initiation Protocol (SIP) SoftwareSource CVE Database V5

Not known to be exploited · CVSS 5.3 Medium.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.1 base score

5.3Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 28% 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:L/A:N

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

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: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 3 Sep 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 2026-10-26.

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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC 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
Cisco Cisco Session Initiation Protocol (SIP) Software	Affected =11.5 =10.3 =10.2 =11.0 =11.7 =12.1 =12.5 =12.6 =12.0 =9.3 =12.7 =12.8 =14.0 =14.1 =14.2 =3.1 =3.0 =2.3 =2.2 =2.1 =2.0 =14.3 =3.2	Fixed in–

AI-suggested

1. Immediately verify whether Web Access is enabled on all Cisco IP phones in the environment. Disable Web Access if it is not strictly necessary for operational purposes. 2. For devices requiring Web Access, restrict access to trusted management networks only, using network segmentation and firewall rules to limit exposure. 3. Apply all available Cisco patches and firmware updates addressing this vulnerability as soon as they become available. Monitor Cisco security advisories closely for patch releases. 4. Implement strict access control policies and multi-factor authentication for any remote management interfaces to reduce the risk of unauthorized access. 5. Conduct regular audits of device configurations and logs to detect any unauthorized file modifications or suspicious activity. 6. Employ network intrusion detection systems (IDS) or intrusion prevention systems (IPS) tuned to detect anomalous SIP or HTTP requests targeting IP phones. 7. Educate IT and security teams about the risks associated with enabling Web Access on IP phones and enforce change management policies to prevent inadvertent exposure. 8. Consider deploying endpoint protection solutions capable of monitoring and alerting on unauthorized file system changes on IP phones where supported.

Description

A vulnerability in the directory permissions of Cisco Desk Phone 9800 Series, Cisco IP Phone 7800 and 8800 Series, and Cisco Video Phone 8875 could allow an unauthenticated, remote attacker to write arbitrary files on an affected device. This vulnerability is due to a lack of proper authentication controls. An attacker could exploit this vulnerability by sending a crafted request to an affected device. A successful exploit could allow the attacker to perform arbitrary file writes to specific directories in the underlying operating system. Note: To exploit this vulnerability, Web Access must be enabled on the phone. Web Access is disabled by default.

Impact

For European organizations, this vulnerability poses a risk primarily to enterprises and public sector entities that deploy Cisco IP phones extensively as part of their unified communications infrastructure. Successful exploitation could allow attackers to modify device files, potentially disrupting voice communications or enabling persistent footholds within corporate networks. This could lead to espionage, interception of sensitive communications, or use of compromised devices as pivot points for broader network attacks. Given the reliance on VoIP systems in sectors such as finance, government, healthcare, and critical infrastructure across Europe, the impact could be significant if exploited at scale. The risk is heightened in environments where Web Access is enabled for remote management without adequate network segmentation or access controls. Additionally, compromised phones could undermine trust in communication systems and cause operational disruptions. However, the absence of known exploits and the default disabled state of Web Access somewhat mitigate immediate widespread impact. Organizations with legacy or unpatched Cisco IP phones remain vulnerable, especially if remote management features are enabled without proper security controls.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-phone-write-g3kcC5Df (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 3 Sep 2025, 18:03 UTC

Technical details

References

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