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Fixed in 2020.1.X

Fixed in 2018.4.X, 2019.3.X



Found in










Issue ID




UnityWebRequest fails to verify certificate when "Let's Encrypt Authority X1" certificate is present in system trust store



Reproduction steps:
1. Open Certificate Manager (In Windows, search for "Manage user certificates" in the Start menu)
2. If present, delete Let's Encrypt Authority X3 certificate under "Current User\Intermediate Certification Authorities\Certificates"
3. If not present, install the Let's Encrypt Authority X1 certificate attached below
4. Open the attached project (
5. Enter Play Mode

Expected result: WebRequest is successful and data is fetched
Actual result: The error "Curl error 51: Cert verify failed: UNITYTLS_X509VERIFY_FLAG_NOT_TRUSTED" is thrown and no data is fetched

Reproduced in: 2018.4.10f1, 2018.4.16f1, 2019.2.7f2, 2019.2.19f1, 2019.3.0b4, 2019.3.0f6, 2020.1.0a4
Not reproducible in: 2017.4.36f1, 2018.4.9f1, 2019.2.7f1, 2019.3.0b3, 2020.1.0a3, 2020.1.0a11, 2020.1.0a21

Regressed in: 2018.4.10f1, 2019.2.7f1, 2019.3.0b3, 2020.1.0a4, most likely caused by Case 1076758

  1. Resolution Note (fix version 2020.1):

    Fixed in 2020.1.0a11

  2. Resolution Note (fix version 2019.3):

    Fixed in 2019.3.3f1

  3. Resolution Note (fix version 2018.4):

    Fixed in 2018.4.18f1

Comments (47)

  1. Daniel1x

    May 08, 2020 13:20

    I also get these errors, version 2019.3.0f3.
    It happened suddenly for some reason and causes Unity to crash.

    Curl error 51: Cert verify failed: UNITYTLS_X509VERIFY_FLAG_EXPIRED

  2. United-Screens

    May 08, 2020 13:20

    Same problem 2019.2.13f. And never had it before, Need urgently a solution or workaround

  3. Djaydino

    May 08, 2020 13:16

    2018.4.13f1 same issue and when playing any scene unity stops working

  4. murat303

    May 08, 2020 13:16

    Same problem in 2019.2.21f1

  5. Djaydino

    May 08, 2020 13:09

    2018.4.13f1 Started to appear in Editor just today.
    just now we went live and have a bug to fix, also when play, the editor stops (but no error)

  6. CinKM4D

    May 08, 2020 13:07

    I started Unity (2019.2 16f1) and about every minute in the console there is this curl error 51.

  7. AmalieKae

    May 08, 2020 13:05

    For anyone who wants to keep working until this is resolved: You can do so by going offline and working without internet. Super cumbersome, but for now it's all I can come up with. (If anyone has a better solution, please let me know!)

  8. AmalieKae

    May 08, 2020 13:01

    I just got the error too. (2019.3.0f6) Left my project alone a while (not touching or changing anything), when I came back after a break, this had started happening. Never seen it before.

  9. Ereona

    May 08, 2020 12:57

    The same error in Unity 2019.2.14f1

  10. jwright_unity

    May 08, 2020 12:57

    started getting the same issue about 30 minutes ago. UNITYTLS_X509VERIFY_FLAG_EXPIRED

    doesn't seem to be project related

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