From 91473381c21a4bbc66e1287ed2a4c8ec48951bca Mon Sep 17 00:00:00 2001 From: Friendly Rabbit <169707731+friendly-rabbit-35@users.noreply.github.com> Date: Mon, 22 Jul 2024 14:58:51 -0700 Subject: [PATCH] Clarify cert pinning in Play Store (addresses https://github.com/PrivSec-dev/privsec.dev/issues/263) Signed-off-by: Friendly Rabbit <169707731+friendly-rabbit-35@users.noreply.github.com> --- content/posts/android/F-Droid Security Issues.md | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/content/posts/android/F-Droid Security Issues.md b/content/posts/android/F-Droid Security Issues.md index f905e85..b41b323 100644 --- a/content/posts/android/F-Droid Security Issues.md +++ b/content/posts/android/F-Droid Security Issues.md @@ -81,7 +81,7 @@ It is also worth noting that the repository metadata format for F-Droid isn't pr F-Droid's official client also lacks **TLS certificate pinning**. Certificate pinning is a way for apps to increase the security of their connection to services [by providing a set of public key hashes](https://developer.android.com/training/articles/security-config#CertificatePinning) of known-good certificates for these services instead of trusting pre-installed CAs. This can avoid some cases where an interception (*man-in-the-middle* attack) could be possible and lead to various security issues, considering you're trusting an app to deliver you other apps. -Certificate pinning is an important security feature that is also straightforward to implement using the [declarative network security configuration](https://developer.android.com/training/articles/security-config) available since Android 7.0 (API level 24). The Play Store uses this feature, which improves security for all connections to Google (they generally use a limited set of root CAs including [their own](https://pki.goog/)). Likewise, see how GrapheneOS pins both root and CA certificates in their [app repository client](https://github.com/GrapheneOS/Apps): +Certificate pinning is an important security feature that is also straightforward to implement using the [declarative network security configuration](https://developer.android.com/training/articles/security-config) available since Android 7.0 (API level 24). The [GrapheneOS App Store](https://github.com/GrapheneOS/AppStore) uses this feature; see how GrapheneOS pins both root and CA certificates in their app repository client: ```xml <!-- res/xml/network_security_config.xml --> @@ -104,6 +104,8 @@ Certificate pinning is an important security feature that is also straightforwar </network-security-config> ``` +The Play Store does not use certificate pinning exactly, but achieves a similar level of security for all connections to Google by using a limited set of root CAs, including [their own](https://pki.goog/)). This practice, alongside the Play Store's use of [package signing](https://source.android.com/docs/security/features/apksigning), guarantees that the apps you download from the Play Store are obtained securely and not tampered with. F-Droid does **not** provide the same guarantee. + To be fair, the F-Droid team has considered several times about adding certificate pinning to their client [at least for the default repositories](https://gitlab.com/fdroid/fdroidclient/-/issues/105). [Relics of preliminary work](https://gitlab.com/fdroid/fdroidclient/-/blob/1.14-alpha4/app/src/main/java/org/fdroid/fdroid/FDroidCertPins.java) can even be found in their current codebase, but it's unfortunate that they haven't been able to find [any working implementation](https://github.com/f-droid/fdroidclient/commit/7f78b46664981b9b73cadbfdda6391f6fe939c77) so far. Given the overly complex nature of F-Droid, that's largely understandable. In a situation where TLS certificate pinning cannot be implemented, though, the next best thing --- rather, the most basic thing --- is to have a robust infrastucture for TLS. This means setting up CAA records with account pinning, setting up DNSSEC, and pinning ACME `accounturi` and `validationmethods`. Other basic security practices within this scope include enforcing TLS 1.2 and TLS 1.3 and disabling weak ciphers. F-Droid does **not** implement **any** of these. They do not have CAA records and DNSSEC and [still support TLS 1.0 and TLS 1.1](https://www.hardenize.com/report/f-droid.org/1721021966#www_tls) with their servers.