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NVD / CVE Program· CNA EEF

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

Noroxi assessment

Priority: Monitor (action score 32/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.97% (FIRST EPSS); higher than 61.9% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Erlang OTP 27.3.4.17, 28.5.0.6, 29.0.6; azl3 erlang 26.2.5.21-4 on Azure Linux 3.0 26.2.5.21-6; azl3 erlang 26.2.5.21-6 on Azure Linux 3.0 26.2.5.21-6.

Low priority for now. Upgrade to Erlang OTP 27.3.4.17, 28.5.0.6, 29.0.6; azl3 erlang 26.2.5.21-4 on Azure Linux 3.0 26.2.5.21-6; azl3 erlang 26.2.5.21-6 on Azure Linux 3.0 26.2.5.21-6 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

HighCVSS 8.2 · v4.0—No exploit Fix available
Published
Sep 1, 2026
Updated
Sep 8, 2026
EPSS
0.9% · 61th percentile

Report tools

JSON

Action score

32

Monitor

Low priority for now.

CVSS
32 / 40 · 8.2 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.9%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · EEF
8.2
NVD has not scored this yet; the score shown is the CNA’s.

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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When you'll hear from us

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (EEF). Independent of NVD's CPE analysis and usually ahead of it.

  • Erlang OTP

    • before 17.0unknown · otp
    • 17.0 and later · before 27.3.4.17affected · otp
    • 28.0 and later · before 28.5.0.6affected · otp
    • 29.0 and later · before 29.0.6affected · otp
    • before 5.10unknown · otp
    • 5.10 and later · before 9.3.2.7affected · otp
    • 9.4 and later · before 9.6.2.3affected · otp
    • 9.7 and later · before 9.7.2affected · otp
    • 84adefa331c4159d432d22840663c38f155cd4c1 and lateraffected · gitfixed in bac19eb3dbd96cc49b6d8cabc1c04248bf8c79f6, d8878dec0ececc2eab18e47bb18b472f224ca633, 9641944a2efbf55bea760f8ff7ba777fe3a0961c

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12erlangfrom 0—
Debian:13erlangbefore 1:27.3.4.1+dfsg-1+deb13u41:27.3.4.1+dfsg-1+deb13u4
Debian:14erlangbefore 1:29.0.6+dfsg-11:29.0.6+dfsg-1
Red Hat:hummingbird:1erlang27before 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-asn1before 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-common_testbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-compilerbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-cryptobefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-debuggerbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-dialyzerbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-diameterbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-edocbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-eldapbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-erl_interfacebefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-ertsbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-etbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-eunitbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-examplesbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-ftpbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-gdb-toolsbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-inetsbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-jinterfacebefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-kernelbefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1
Red Hat:hummingbird:1erlang27-megacobefore 0:27.3.4.17-0.1.hum10:27.3.4.17-0.1.hum1

+18

Same product

erlang: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-89422TLS 1.3 client skips server authentication when ServerHello carries an unsolicited pre_shared_key extension
    37Monitor
  • CVE-2026-74835inets,httpd: Memory Exhaustion via Unenforced max_body_size During Chunked Body Reception
    34Monitor
  • CVE-2026-71380httpd applies no timeout while receiving a request body, parking a worker on a stalled client
    34Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-59696Sep 1, 2026 · uri_string does not bound the port component of a URI before integer conversion
    27Monitor
  • ← EarlierCVE-2026-66357Sep 1, 2026 · inets,httpd:HTTP Request Smuggling via obs-fold Header Continuation
    33Monitor
  • Later →CVE-2026-69664Sep 1, 2026 · httpd parks a request worker indefinitely on a malformed chunk size sent after the headers
    34Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Erlang OTP27.3.4.17Vendor (CNA)
Erlang OTP28.5.0.6Vendor (CNA)
Erlang OTP29.0.6Vendor (CNA)
Erlang OTP9.3.2.7Vendor (CNA)
Erlang OTP9.6.2.3Vendor (CNA)
Erlang OTP9.7.2Vendor (CNA)
Erlang OTP9641944a2efbf55bea760f8ff7ba777fe3a0961cVendor (CNA)
Erlang OTPbac19eb3dbd96cc49b6d8cabc1c04248bf8c79f6Vendor (CNA)
Erlang OTPd8878dec0ececc2eab18e47bb18b472f224ca633Vendor (CNA)
azl3 erlang 26.2.5.21-4 on Azure Linux 3.026.2.5.21-6Microsoft (MSRC)
azl3 erlang 26.2.5.21-6 on Azure Linux 3.026.2.5.21-6Microsoft (MSRC)
debian:erlang1:27.3.4.1+dfsg-1+deb13u4 · Debian:13Package registry (OSV)
debian:erlang1:29.0.6+dfsg-1 · Debian:14Package registry (OSV)
red hat:erlang270:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-asn10:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-common_test0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-compiler0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-crypto0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-debugger0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-dialyzer0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-diameter0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-edoc0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-eldap0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-erl_interface0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:erlang27-erts0:27.3.4.17-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-50 · Path Equivalence: '//multiple/leading/slash'

CVSS vector

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (6 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records