Sandbox::https://github.com/curl/curl/pull/23277

vszakats · 2026-10-06T01:28:50Z

Previous default was to search for a CA bundle (curl-ca-bundle.crt) in
a list of directories, including CWD and PATH, which allowed an
attacker to place a CA bundle there and the curl tool picking it up.
(Unless Native CA was enabled at build time, which disables on-disk CA
bundle searches by default.)

Change the default to search for a CA bundle in the curl tool directory
only.

Note: This is a breaking change for curl builds using a non-Schannel TLS
backend, with Native CA and embedded CA disabled and with a
curl-ca-bundle.crt CA bundle file missing from the directory of
curl.exe. To remedy, copy or download a valid CA bundle into the
curl.exe directory.

To keep old (insecure) behavior, build curl with:

autotools: --disable-ca-search-safe
cmake: -DCURL_CA_SEARCH_SAFE=OFF

Safe alternatives are Native CA, embedded CA, or Schannel if the
use-case allows.

Also:

make sure to disable safe search option by default if native CA is
enabled. To keep existing behavior.
drop the option to enable safe search for Windows UWP builds.
To keep existing behavior of not doing on-disk search, and to
simplify.
remove disable-CA-search option for UWP builds. It's a no op,
(unsafe) search is not supported on UWP because the necessary Win32
API (SearchPath()) is not provided by the OS.

Reported-by: Joshua Rogers
Follow-up to 22652a5 #14582

https://github.com/curl/curl/pull/23277/files?w=1

curl-for-win has been shipping with CA bundle embedded since 8.10.0
(2024-09-11). It first did an unsafe search, and if not found a CA
bundle fell back to the embedded one. Since 8.19.0 (2026-03-11)
curl-for-win ships with Native CA and on-disk CA search disabled.
It also had safe CA search enabled in daily builds since 8.10.0-dev.

maybe add Unicode support to tool_execpath()? or keep disabled
in Unicode builds (which would be a shame IMO).
perhaps break out the tool_execpath() patch into a separate PR. → tool_util: add Unicode support to tool_execpath() #23287
rebase on tool_util: add Unicode support to tool_execpath() #23287.
maybe keep safe search disabled for UWP, where the pre-existing
behavior was: no search (because the necessary Win32 API is
not available for UWP). Kind of corner or corner case, there seems
to be almost (?) nobody using UWP, and especially nobody using
the curl tool in UWP mode.

jay · 2026-10-06T06:01:34Z

In my opinion this isn't a vulnerability in curl and limiting the search path by default is likely to break some scripts using the documented behavior. --cacert currently says:

(Windows) curl automatically looks for a CA certs file named 'curl-ca-bundle.crt', either in the same directory as curl.exe, or in the Current Working Directory, or in any folder along your PATH.

That and the next paragraph explaining the build option would need to be updated to explain it is now limited by default. I'm not really against this but not really for it either.

edit: also you will need to update this section in SSLCERTS

curl#23277 (comment)

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To fix opening `.curlrc`/`_curlrc` next to the curl tool, and to make the CA safe search built-time option work as expected when the curl tool resides on a non-ASCII path. Follow-up to d40f4e1 Follow-up to 78882e4 Cherry-picked from curl#23277

To fix opening `.curlrc`/`_curlrc` next to the curl tool, and to make the CA safe search built-time option find `curl-ca-bundle.crt` as expected when the curl tool resides on a non-ASCII path when using a Unicode-enabled build. The CA safe search build-time option is disabled by default. The issue has been discovered while working on enabling it by default. Follow-up to d40f4e1 Follow-up to 78882e4 Cherry-picked from #23277 Closes #23287

CURL_CA_NATIVE defaults OFF, so CURL_DISABLE_CA_SEARCH also defaults OFF, and CURL_CA_SEARCH_SAFE previously defaulted OFF too. That left the unsafe curl-ca-bundle.crt lookup via SearchPath() (application directory, CWD, Windows directories, then every %PATH% entry) enabled by default in Windows CMake builds. A local attacker able to place curl-ca-bundle.crt in the current directory or an earlier attacker-writable PATH directory could get an ordinary curl invocation to trust an attacker-controlled root CA. Default CURL_CA_SEARCH_SAFE to ON so the existing safe search (limited to the curl tool's own directory) is used unless a user explicitly opts back into the legacy CWD/PATH search with -DCURL_CA_SEARCH_SAFE=OFF. Reported-by: Joshua Rogers

Native Windows builds enabled the unsafe SearchPath()-based CA bundle discovery by default, unless the native CA store was requested with --enable-ca-native. SearchPath() checks the application directory and the current working directory before the Windows system directories and %PATH%, so a local attacker able to place curl-ca-bundle.crt in a victim's current directory, or an earlier %PATH% entry, could make curl trust an attacker-controlled root CA without --cacert or --insecure ever being used. Default --enable-ca-search-safe to on, so the tool directory only search (CURL_CA_SEARCH_SAFE) is used unless a builder opts out with --disable-ca-search-safe. This takes precedence over the unsafe CWD/PATH search regardless of --enable-ca-search, so the old default behavior now requires an explicit --disable-ca-search-safe. Reported-by: Joshua Rogers

curl#23277 (comment)

… it now

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Copilot review overview

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No blocking issues were identified; only a minor documentation clarification remains.

Review effort: Lite
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Resolved since last review (1)

Force CURL_CA_SEARCH_SAFE off for UWP builds

vszakats · 2026-10-06T21:13:44Z

I addressed the missing documentation updates. Also fixed a worker function
used in safe-search codepath that lacked Unicode support (#23287). Ironed
out legit UWP concerns raised by the LLM, and fixed to not enable safe-search
by default if Native CA is enabled.

jay · 2026-10-11T19:41:19Z

This is another one I suggest wait until the next feature window.

vszakats · 2026-10-11T20:09:44Z

This is another one I suggest wait until the next feature window.

Agree, this one is definitely for the next cycle.

vszakats added TLS Windows Windows-specific labels Oct 6, 2026

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vszakats added a commit to vszakats/curl that referenced this pull request Oct 6, 2026

cm fix to disable safe search with Native CA enabled at build-time

df382d4

curl#23277 (comment)

vszakats added a commit to vszakats/curl that referenced this pull request Oct 6, 2026

am step2: disable safe search if native ca is enabled

51b35a0

curl#23277 (comment)

vszakats force-pushed the safe-ca branch 2 times, most recently from daf3e91 to 5faace5 Compare October 6, 2026 10:34

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vszakats mentioned this pull request Oct 6, 2026

tool_util: add Unicode support to tool_execpath() #23287

Closed

MegaManSec and others added 17 commits October 6, 2026 22:50

appveyor.sh point to CA bundle

decb975

cacert.md update

3ca3b59

SSLCERTS.md update

02cc663

cm fix to disable safe search with Native CA enabled at build-time

dabb08b

curl#23277 (comment)

am step1

c37e5ca

am step2: disable safe search if native ca is enabled

a3f35b9

curl#23277 (comment)

cm fix to disable safe search with Native CA enabled at build-time docs

bd7bc55

am drop support for safe search on UWP

9239a8a

cm drop support for safe search on UWP

6e31aed

cm also drop no-op CURL_DISABLE_CA_SEARCH on UWP

cb7f280

am disable no-op --enable-ca-search for UWP to sync with cmake

c2e6121

pyspelling.words UWP

f329c55

CMakeLists.txt cm fold long line

b61d6a3

INSTALL-CMAKE.md: drop mentions of UWP, overkill to start documenting…

9675255

… it now

am fixup

a60044c

vszakats force-pushed the safe-ca branch from 6cff0b4 to a60044c Compare October 6, 2026 20:50

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build: enable safe CA search by default (Windows) - #23277

build: enable safe CA search by default (Windows)#23277
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