math/big: panic during recursive division of very large numbers #42552
A number of math/big.Int methods (Div, Exp, DivMod, Quo, Rem, QuoRem, Mod, ModInverse, ModSqrt, Jacobi, and GCD) can panic when provided crafted large inputs. For the panic to happen, the divisor or modulo argument must be larger than 3168 bits (on 32-bit architectures) or 6336 bits (on 64-bit architectures). Multiple math/big.Rat methods are similarly affected.
crypto/rsa.VerifyPSS, crypto/rsa.VerifyPKCS1v15, and crypto/dsa.Verify may panic when provided crafted public keys and signatures. crypto/ecdsa and crypto/elliptic operations may only be affected if custom CurveParams with unusually large field sizes (several times larger than the largest supported curve, P-521) are in use. Using crypto/x509.Verify on a crafted X.509 certificate chain can lead to a panic, even if the certificates don’t chain to a trusted root. The chain can be delivered via a crypto/tls connection to a client, or to a server that accepts and verifies client certificates. net/http clients can be made to crash by an HTTPS server, while net/http servers that accept client certificates will recover the panic and are unaffected.
Moreover, an application might crash invoking crypto/x509.(*CertificateRequest).CheckSignature on an X.509 certificate request or during a golang.org/x/crypto/otr conversation. Parsing a golang.org/x/crypto/openpgp Entity or verifying a signature may crash. Finally, a golang.org/x/crypto/ssh client can panic due to a malformed host key, while a server could panic if either PublicKeyCallback accepts a malformed public key, or if IsUserAuthority accepts a certificate with a malformed public key.
Thanks to the Go Ethereum team and the OSS-Fuzz project for reporting this. Thanks to Rémy Oudompheng and Robert Griesemer for their help developing and validating the fix.
This issue is CVE-2020-28362.
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I can confirm that the issue does not impact versions prior to 1.14. However, please note the official policy:
This means that right now we support only Go 1.15 and Go 1.14, and that Go 1.13 is unsupported and it won't receive backports for security fixes.
We typically don't research or document the impact of vulnerabilities on unsupported versions of Go, since that is outside the scope of responsibility for the team.
The vulnerability that allowed this panic is CVE-2020-28362 and has been fixed in a security release, per #42552. Change-Id: I774bcda2cc83cdd5a273d21c8d9f4b53fa17c88f Reviewed-on: https://go-review.googlesource.com/c/go/+/277959 Run-TryBot: Katie Hockman <firstname.lastname@example.org> TryBot-Result: Go Bot <email@example.com> Trust: Katie Hockman <firstname.lastname@example.org> Reviewed-by: Filippo Valsorda <email@example.com>