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CVE-2026-45100— OpenSIPS: Buffer Overflow in Base64 Encode Transformation

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 3.4.0-beta版本至3.6.6之前版本和4.0.0-beta版本至4.0.0-rc1之前版本存在缓冲区错误漏洞，该漏洞源于{s.b64encode}字符串转换过程中存在缓冲区溢出，base64编码扩展数据导致溢出，可能破坏相邻缓冲区数据，远程攻击者可通过发送包含大头部值的SIP消息触发。

CVSS 9.1 · Critical EPSS 0.83% · P56

Affected Version Matrix 2

VendorProduct Version RangeStatus
OpenSIPS opensips >= 3.4.0-beta, < 3.6.6 affected
>= 4.0.0-beta, < 4.0.0-rc1 affected
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I. Basic Information for CVE-2026-45100

Vulnerability Information
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Vulnerability Title
OpenSIPS: Buffer Overflow in Base64 Encode Transformation
Source: CVE Program / CVE List V5
Vulnerability Description
OpenSIPS is a Session Initiation Protocol (SIP) server implementation. Versions 3.4.0-beta through 3.6.5 and 4.0.0-beta contain a buffer overflow in the {s.b64encode} string transformation. The size check for {s.b64encode} only verifies that the input fits within the 64 KB transformation buffer, but base64 encoding expands the data by roughly a third, so an input between about 49,153 and 65,535 bytes produces more output than the buffer can hold and overflows it by up to 21,844 bytes. Because these transformation buffers sit next to each other in memory and are reused for chained transformations, the overflow writes attacker-controlled data into the adjacent buffer and corrupts values used by later transformations processing the same SIP message. A remote attacker can trigger this by sending a SIP message with a large header value (roughly 50,000 bytes or more) when the routing script applies  {s.b64encode}  to attacker-controlled input, making exploitability dependent on the deployment's routing configuration. 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 3.4.0-beta版本至3.6.6之前版本和4.0.0-beta版本至4.0.0-rc1之前版本存在缓冲区错误漏洞，该漏洞源于{s.b64encode}字符串转换过程中存在缓冲区溢出，base64编码扩展数据导致溢出，可能破坏相邻缓冲区数据，远程攻击者可通过发送包含大头部值的SIP消息触发。
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-beta, < 3.6.6 -

II. Public POCs for CVE-2026-45100

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 10432 chars
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III. Intelligence Information for CVE-2026-45100

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Patches & Fixes for CVE-2026-45100 (2)

Vendor Advisories for CVE-2026-45100 (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-2026-45537 9.1 CRITICAL OpenSIPS: Global Buffer Overflow in construct_uri
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-2026-45100

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