GHSA-rm3j-f69w-wqmq CVE-2026-39834 GO-2026-5020

golang.org/x/crypto vulnerable to infinite loop on large channel writes

Critical Go

Severity: 9.1 / 10; Critical · CVSS 3.1
Exploit chance (EPSS): 0.60%; Chance of exploitation in the next 30 days. Higher than 48.59% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-190 Integer Overflow or Wraparound
Fix: 0.52.0; Upgrade golang.org/x/crypto to this version or later

Description

When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation.

Affected versions

Go

Package	Vulnerable	Fixed in
golang.org/x/crypto	`< 0.52.0`	`0.52.0`
golang.org/x/crypto	`< 0.52.0`	`0.52.0`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

golang.org/x/crypto Go → `0.52.0`

go

go get golang.org/x/crypto@v0.52.0 && go mod tidy

Severity breakdown

CVSS 3.1 9.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: High

Weakness

CWE-190: Integer Overflow or Wraparound

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.

How to prevent it

Requirements: Ensure that all protocols are strictly defined, such that all out-of-bounds behavior can be identified simply, and require strict conformance to the protocol.
Requirements: Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. If possible, choose a language or compiler that performs automatic bounds checking.
Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482]. Use libraries or frameworks that make it easier to handle numbers without unexpected consequences. Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]
Implementation: Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range. Use unsigned integers where possible. This makes it easier to perform validation for integer overflows. When signed integers are required, ensure that the range check includes minimum values as well as maximum values.
Implementation: Understand the programming language's underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, "not-a-number" calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-7] Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.
Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Implementation: Examine compiler warnings closely and eliminate problems with potential security implications, such as signed / unsigned mismatch in memory operations, or use of uninitialized variables. Even if the weakness is rarely exploitable, a single failure may lead to the compromise of the entire system.

References

Advisories

Packages

cs.opensource.google/go/x/crypto

Timeline

May 22, 2026 Published
Sep 22, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GO-2026-6355 Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh	High	Also affects golang.org/x/crypto
GO-2026-6354 Prevent DoS on deadlocked undecided channel in golang.org/x/crypto/ssh	High	Also affects golang.org/x/crypto
GO-2026-6303 Source-address critical option not enforced for non-public-key auth callbacks in golang.org/x/crypto/ssh	High	Also affects golang.org/x/crypto
GO-2026-5932 The golang.org/x/crypto/openpgp package is unmaintained, unsafe by design, and has known security issues	Not rated yet	Also affects golang.org/x/crypto
GHSA-x527-x647-q7gg golang.org/x/crypto: Invoking VerifiedPublicKeyCallback permissions skip enforcement	Critical	Also affects golang.org/x/crypto
GHSA-w879-237q-wc7r golang.org/x/crypto: Invoking pathological RSA/DSA parameters may cause DoS	High	Also affects golang.org/x/crypto
GHSA-vgwf-h737-ff37 golang.org/x/crypto: Invoking client can cause server deadlock on unexpected responses	Critical	Also affects golang.org/x/crypto
GHSA-qpw4-5x99-6vjp golang.org/x/crypto: Invoking memory leak when rejecting channels can lead to DoS	Medium	Also affects golang.org/x/crypto

Credits: NCC Group Cryptography Services, sponsored by Teleport

Is this in your code?

MergeHarbor checks every repository's dependencies against this database, ranks what matters by exploitability and reachability, routes it to the owning team and opens the fix pull request.

Check your repos with MergeHarbor