CVE-2023-41763VulnerabilityPublished 10 Oct 2023Updated 21 Oct 2025

CVE-2023-41763: Microsoft Skype for Business Server 2015 CU13 · Server-Side Request Forgery (SSRF)

Affects Microsoft Skype for Business Server 2015 CU13Source CVE Database V5

Exploited in the wild · KEV due 31 Oct 2023 · public detection template (Nuclei) · 90% EPSS : apply the vendor's fix or mitigations to Microsoft Skype for Business Server 2015 CU13 now.

Data as of 26 Oct 2026, 07:57 UTC

CVSS 3.1 base score

5.3Medium

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

KEV deadline: 31 Oct 2023 US federal agencies must patch by this date; a sensible deadline for everyone else.
EPSS: 90.5% chance of exploitation in 30 days – higher than 99% 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:L/I:N/A:N/E:P/RL:O/RC:C

Base metrics

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

Temporal metrics

Exploit Code Maturity: Proof-of-Concept
Remediation Level: Official Fix
Report Confidence: Confirmed

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: None: There is no impact to availability within the impacted component.
Exploit Code Maturity: Proof-of-Concept: Proof-of-concept exploit code is available, or an attack demonstration is not practical for most systems. The code or technique is not functional in all situations and may require substantial modification by a skilled attacker.
Remediation Level: Official Fix: A complete vendor solution is available. Either the vendor has issued an official patch, or an upgrade is available.
Report Confidence: Confirmed: Detailed reports exist, or functional reproduction is possible (functional exploits may provide this). Source code is available to independently verify the assertions of the research, or the author or vendor of the affected code has confirmed the presence of the vulnerability.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 10 Oct 2023
Detectable: evidence found.
nuclei template: Skype for Business 2019 (SfB) - Blind Server-side Request Forgery
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: evidence found.
Listed in CISA KEV the same day as disclosure
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

CVE ID reserved
by microsoft
2023-08-3123:08Z, 40 days before disclosure
CVE published
on cve.org
2023-10-1017:07Z, t = 0
Added to CISA KEV (opens in a new tab)
exploitation confirmed
2023-10-10, the same day as disclosure
KEV remediation due
US federal deadline
2023-10-31, 21 days after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA KEV (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

Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Affected software

Product	Affected	Fixed in
Microsoft Skype for Business Server 2015 CU13	Affected =9319.0	Fixed in–

Description

Skype for Business Elevation of Privilege Vulnerability

Impact

For European organizations, this vulnerability poses a risk primarily to confidentiality, as attackers can potentially access internal resources or sensitive information by exploiting the SSRF flaw. Organizations using Skype for Business Server 2015 CU13 may face unauthorized data disclosure, which could lead to compliance violations under GDPR if personal or sensitive data is exposed. Although the vulnerability does not directly affect system integrity or availability, the information gained through SSRF could facilitate further attacks, including privilege escalation or lateral movement within the network. Enterprises with critical internal services accessible only via the Skype for Business Server could see increased risk. The absence of known exploits reduces immediate risk, but the ease of exploitation without authentication means attackers could quickly develop weaponized exploits. This is particularly concerning for sectors with high regulatory and security requirements such as finance, healthcare, and government institutions across Europe.

Mitigation

Since no official patches are currently linked, European organizations should implement immediate compensating controls. These include restricting outbound HTTP requests from the Skype for Business Server to only trusted internal and external endpoints via firewall rules or network segmentation. Monitoring and logging all outgoing requests from the server can help detect suspicious activity indicative of SSRF exploitation attempts. Organizations should also review and harden internal services accessible through the Skype for Business Server to minimize sensitive data exposure. Applying the latest cumulative updates for Skype for Business Server 2015 as they become available is critical. Additionally, consider isolating the Skype for Business Server in a dedicated network segment with strict access controls. Conduct regular vulnerability scanning and penetration testing focused on SSRF vectors. Finally, prepare incident response plans to quickly address any exploitation attempts.

CWE-918Server-Side Request Forgery (SSRF) (opens in a new tab)
Base weaknessCWE Top 25 (2025): #22OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
OWASP Cheat Sheets
Server Side Request Forgery Prevention (opens in a new tab)
Unvalidated Redirects and Forwards (opens in a new tab)
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V12.6.1 (opens in a new tab)
V5.2.6 (opens in a new tab)
Attack patterns
Server Side Request Forgery (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

Timeline

What to do

Affected software

Description

AI analysisMachine-generated, updated 21 Oct 2025, 20:15 UTC

Public exploits and detectiona Nuclei detection template

WeaknessesCWE-918

Technical details

References

Community reviews

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