VulnerabilityPublished 17 Jun 2026Updated 4 Aug 2026

CVE-2026-48818: Kludex starlette · Server-Side Request Forgery (SSRF)

Affects Kludex starletteSource CVE Database V5

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Not known to be exploited · CVSS 7.5 High : upgrade to 1.1.0 soon.

Data as of 31 Oct 2026, 08:20 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 30% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.1.0

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within 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 17 Jun 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 30 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

Upgrade Kludex starlette to 1.1.0.

Affected software

Product	Affected	Fixed in
Kludexstarlette	Affected <1.1.0	Fixed in 1.1.0
PyPIstarlette`pkg:pypi/starlette`Other threats	Affected <1.1.0	Fixed in 1.1.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in Starlette version 1.1.0. Users should upgrade to version 1.1.0 or later to remediate this vulnerability. Red Hat advisories state that their products are not affected and do not provide a mitigation for this issue. No alternative mitigations meeting Red Hat's criteria are currently available. Users on Windows should avoid using vulnerable versions and consider enabling follow_symlink=true if applicable, though the primary remediation is upgrading Starlette.

Description

### Summary When serving static files on Windows, `StaticFiles` resolves the requested path with [`os.path.realpath`](https://docs.python.org/3/library/os.path.html#os.path.realpath). If a UNC path (such as `\\attacker.com\share`) reaches the resolver, `realpath` causes the process to open a connection to the remote host over SMB (port 445). This is a server-side request forgery (SSRF) that leaks the service account's NTLMv2 credentials to the attacker-controlled host, which can then be cracked offline or relayed to other hosts. ### Details `StaticFiles.lookup_path()` joins the requested path onto the served directory and calls [`os.path.realpath`](https://docs.python.org/3/library/os.path.html#os.path.realpath) on the result before checking containment with [`os.path.commonpath`](https://docs.python.org/3/library/os.path.html#os.path.commonpath). On Windows, a UNC path is absolute, so [`os.path.join`](https://docs.python.org/3/library/os.path.html#os.path.join) discards the served directory and `realpath` resolves the bare UNC path, triggering the outbound SMB connection and NTLM authentication before the containment check rejects the path. The HTTP response is a benign 404, but the credential disclosure has already happened. POSIX systems are not affected. This only affects the default configuration (`follow_symlink=False`), which uses [`os.path.realpath`](https://docs.python.org/3/library/os.path.html#os.path.realpath). The `follow_symlink=True` branch uses [`os.path.abspath`](https://docs.python.org/3/library/os.path.html#os.path.abspath), which performs no I/O. ### Impact Applications running on Windows that serve files with `StaticFiles` (directly, or via a framework built on Starlette such as FastAPI) in the default configuration are affected. `StaticFiles` is typically unauthenticated, so any client can trigger the SMB connection and leak the service account's NTLMv2 hash. A secondary impact is discovering internal hosts reachable over SMB by timing responses for valid versus invalid addresses. ### Mitigation Applications not running on Windows are not affected. On Windows, serving static files through a dedicated web server (such as nginx or IIS) instead of `StaticFiles` avoids the issue. Blocking outbound SMB (port 445) from the application host prevents the credential disclosure even if a UNC path is resolved.

Impact

The vulnerability allows remote attackers to cause the server to initiate outbound SMB connections, potentially exposing NTLMv2 credentials of the service account. These credentials can be captured for offline cracking or relay attacks, leading to confidentiality breaches. The vulnerability does not impact integrity or availability. It is specific to Windows environments and default follow_symlink=false deployments. Red Hat products are not affected as they do not include the vulnerable code or run on Windows.

Summary

Starlette versions 1.0.1 and earlier on Windows are vulnerable to SSRF via the StaticFiles component when handling UNC paths. An attacker can cause the server to initiate an outbound SMB connection by providing a UNC path such as \\attacker.com\share, which leads to exposure of the service account's NTLMv2 credentials despite the HTTP response being a 404. This vulnerability affects default deployments with follow_symlink=false, including frameworks built on Starlette like FastAPI. POSIX systems and deployments with follow_symlink=true are not affected. The issue is resolved in version 1.1.0 of Starlette. Red Hat advisories confirm that their products are not impacted due to platform and configuration differences.

CWE-918Server-Side Request Forgery (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.
Implementation · Operation
If there is a known list of applications, IP, hostname, and/or domains to which the product is allowed to communicate, then use allowlists to ensure that outgoing requests are restricted to these known entities. The allowlists could be in the application code or possibly enforced by firewalls or network segmentation.
Implementation · Operation
If the product is expected to be able to connect to arbitrary IP addresses or domains, consider using a denylist that includes private network addresses, internal domain names, etc. The denylist could be in the application code or possibly enforced by firewalls or network segmentation.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
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).

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What to do

Affected software

Description

AI analysisMachine-generated, updated 5 Aug 2026, 13:33 UTC

WeaknessesCWE-918

Technical details

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