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CVE-2026-66835— httpd mod_auth directory protection bypassed by a doubled slash in the request path

Quick assessment

Affected
Erlang OTP
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Erlang/OTP是Erlang/OTP团队开源的一个JavaScript编写的处理处理异常的库。该库可以捕捉node.js内置API引发的异常。 Erlang/OTP inets httpd 17.0版本至27.3.4.17之前版本、28.0版本至28.5.0.6之前版本和29.0版本至29.0.6之前版本存在路径遍历漏洞，该漏洞源于URI规范化时未折叠空路径段，导致双斜杠绕过mod_auth目录保护，远程未授权攻击者可读取受保护目录中的文件。

CVSS 8.2 · High EPSS 0.97% · P62

Possible ATT&CK Techniques 2 AI

T1083 · File and Directory Discovery T1544

Affected Version Matrix 9

VendorProduct Version RangeStatus
Erlang OTP < 17.0 unknown
17.0< 27.3.4.17 affected
28.0< 28.5.0.6 affected
29.0< 29.0.6 affected
< 5.10 unknown
5.10< 9.3.2.7 affected
9.4< 9.6.2.3 affected
9.7< 9.7.2 affected
… +1 more rows
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I. Basic Information for CVE-2026-66835

Vulnerability Information
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Vulnerability Title
httpd mod_auth directory protection bypassed by a doubled slash in the request path
Source: CVE Program / CVE List V5
Vulnerability Description
Path Equivalence vulnerability in Erlang/OTP inets httpd allows a remote unauthenticated attacker to read files inside a mod_auth protected directory by prefixing the request path with an extra slash. httpd_request:validate_uri/1 normalises the request URI with uri_string:normalize/1, which performs RFC 3986 dot-segment removal but does not collapse empty path segments, so a doubled slash survives. mod_alias:real_name/3 concatenates the document root with that URI, and mod_auth:secret_path/3 then decides whether the result lies inside a protected directory block by running the configured directory path as an unanchored regular expression against it. The doubled slash breaks the contiguous substring the regex needs, so the request is treated as unprotected and no authentication challenge is issued, while mod_get opens the same path and the operating system collapses the doubled slash and returns the protected file. The same path mismatch also evades the per-path accounting in mod_security. This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
路径等价：’//multiple/leading/slash’
Source: CVE Program / CVE List V5
Vulnerability Title
Erlang/OTP 路径遍历漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Erlang/OTP是Erlang/OTP团队开源的一个JavaScript编写的处理处理异常的库。该库可以捕捉node.js内置API引发的异常。 Erlang/OTP inets httpd 17.0版本至27.3.4.17之前版本、28.0版本至28.5.0.6之前版本和29.0版本至29.0.6之前版本存在路径遍历漏洞，该漏洞源于URI规范化时未折叠空路径段，导致双斜杠绕过mod_auth目录保护，远程未授权攻击者可读取受保护目录中的文件。
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
Erlang OTP 17.0 ~ 27.3.4.17 cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
Erlang OTP 5.10 ~ 9.3.2.7 cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
Erlang OTP 84adefa331c4159d432d22840663c38f155cd4c1 ~ * cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-66835

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III. Intelligence Information for CVE-2026-66835

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Patches & Fixes for CVE-2026-66835 (3)

Vendor Advisories for CVE-2026-66835 (3)

Same Patch Batch · Erlang · 2026-09-01 · 16 CVEs total

CVE-2026-71380 8.7 HIGH httpd applies no timeout while receiving a request body, parking a worker on a stalled cli
CVE-2026-70399 8.7 HIGH httpd does not enforce the documented default max_clients connection limit
CVE-2026-74835 8.7 HIGH inets,httpd: Memory Exhaustion via Unenforced max_body_size During Chunked Body Reception
CVE-2026-69664 8.7 HIGH httpd parks a request worker indefinitely on a malformed chunk size sent after the headers
CVE-2026-66357 8.3 HIGH inets,httpd:HTTP Request Smuggling via obs-fold Header Continuation
CVE-2026-73812 8.3 HIGH inets, httpd: HTTP Request Smuggling via Transfer-Encoding and Content-Length
CVE-2026-73276 8.3 HIGH inets, httpd: HTTP Request Smuggling via Whitespace-Before-Colon Header Dropping i
CVE-2026-55951 8.2 HIGH httpc memory exhaustion via unbounded response header accumulation
CVE-2026-75538 8.2 HIGH A Signed Length Overflow in Erlang/OTP's inet TCP Driver Overflows the Receive Buffer Into
CVE-2026-73270 8.2 HIGH httpd mod_auth directory protection bypassed by request path casing on case-insensitive fi
CVE-2026-59696 6.9 MEDIUM uri_string does not bound the port component of a URI before integer conversion
CVE-2026-71562 6.3 MEDIUM httpc does not bound server-supplied numeric header values before integer conversion
CVE-2026-70405 6.3 MEDIUM snmp BER INTEGER decoder applies no size limit to attacker-supplied integer fields
CVE-2026-70409 6.3 MEDIUM eldap does not bound the port component of a referral URL before integer conversion
CVE-2026-74994 6.0 MEDIUM inets, httpd: Authentication Bypass via Directory Namespace Collapse in httpd mod_auth

IV. Related Vulnerabilities

Same product: OTP
Same vendor: Erlang
Same weakness: CWE-50