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CVE-2026-45537— OpenSIPS: Global Buffer Overflow in construct_uri

Quick assessment

Affected
OpenSIPS opensips
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

OpenSIPS是OpenSIPS组织开源的一个 GPL 许可的 SIP 服务器实现。 OpenSIPS 3.6.6之前版本和4.0.0-rc1之前版本存在缓冲区错误漏洞，该漏洞源于construct_uri()函数将多个URI组件连接到固定1024字节全局缓冲区时未进行边界检查，可能导致缓冲区溢出，破坏相邻全局数据并改变服务器路由行为。

CVSS 9.1 · Critical EPSS 0.63% · P49

Affected Version Matrix 2

VendorProduct Version RangeStatus
OpenSIPS opensips >= 3.4.0, < 3.6.6 affected
>= 4.0.0-beta, < 4.0.0-rc1 affected
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I. Basic Information for CVE-2026-45537

Vulnerability Information
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Vulnerability Title
OpenSIPS: Global Buffer Overflow in construct_uri
Source: CVE Program / CVE List V5
Vulnerability Description
OpenSIPS is a Session Initiation Protocol (SIP) server implementation. In versions prior to 3.6.6 and 4.0.0-rc1, the construct_uri() function concatenates multiple URI components (protocol, username, domain, port, params) into a fixed 1024-byte global BSS buffer without any bounds checking. When a routing script calls construct_uri() with an attacker-controlled username, a combined component length exceeding 1024 bytes overflows the buffer, corrupting adjacent global data with attacker-controlled content. The overflow reaches disable_503_translation, a global flag controlling SIP 503 response handling, allowing an attacker to deterministically set the flag via the URI username and alter the server's routing behavior for subsequent messages. Because the same buffer is shared with contact_builder(), the overflow also corrupts that function's data, and without a memory sanitizer the adjacent globals are silently overwritten on every request containing a long username. This issue has been fixed in versions 3.6.6 and 4.0.0-rc1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未进行输入大小检查的缓冲区拷贝(传统缓冲区溢出)
Source: CVE Program / CVE List V5
Vulnerability Title
OpenSIPS 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
OpenSIPS是OpenSIPS组织开源的一个 GPL 许可的 SIP 服务器实现。 OpenSIPS 3.6.6之前版本和4.0.0-rc1之前版本存在缓冲区错误漏洞，该漏洞源于construct_uri()函数将多个URI组件连接到固定1024字节全局缓冲区时未进行边界检查，可能导致缓冲区溢出，破坏相邻全局数据并改变服务器路由行为。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
OpenSIPS opensips >= 3.4.0, < 3.6.6 -

II. Public POCs for CVE-2026-45537

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Qwen3.6-35B-A3B · 9489 chars
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III. Intelligence Information for CVE-2026-45537

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Patches & Fixes for CVE-2026-45537 (2)

Vendor Advisories for CVE-2026-45537 (1)

Same Patch Batch · OpenSIPS · 2026-08-04 · 8 CVEs total

CVE-2026-45538 9.8 CRITICAL OpenSIPS: Stack Buffer Overflow in sip_to_json() Header Name Copy
CVE-2026-45100 9.1 CRITICAL OpenSIPS: Buffer Overflow in Base64 Encode Transformation
CVE-2026-45084 8.7 HIGH OpenSIPS: Denial of service in presence.handle_publish() from unchecked Content-Type state
CVE-2026-45809 8.7 HIGH OpenSIPS: Denial of Service in watcherinfo XML generation from oversized watcher URI
CVE-2026-46334 8.7 HIGH OpenSIPS: Denial of Service in SDP bandwidth parsing via QoS SDP cloning
CVE-2026-45103 7.5 HIGH OpenSIPS: SIP Message Smuggling via TCP Content-Length Integer Overflow
CVE-2026-45705 5.3 MEDIUM OpenSIPS: OOB Read in Multipart Body Boundary Parsing

IV. Related Vulnerabilities

Same product: opensips
Same vendor: OpenSIPS
Same weakness: CWE-120

V. Comments for CVE-2026-45537

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