GHSA-vgwf-h737-ff37 CVE-2026-39830 GO-2026-5017

golang.org/x/crypto: Invoking client can cause server deadlock on unexpected responses

Critical Go

Severity: 9.1 / 10; Critical · CVSS 3.1
Exploit chance (EPSS): 0.68%; Chance of exploitation in the next 30 days. Higher than 52.54% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer; CWE-772 Missing Release of Resource after Effective Lifetime
Fix: 0.52.0; Upgrade golang.org/x/crypto to this version or later

Description

A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine could not be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded.

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:H/I:N/A:H

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

Weakness

CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

How to prevent it

Requirements: Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
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. Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.
Operation, Build and Compilation: Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
Implementation: Consider adhering to the following rules when allocating and managing an application's memory: Double check that the buffer is as large as specified. When using functions that accept a number of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the source buffer size, it may not NULL-terminate the string. Check buffer boundaries if accessing the buffer in a loop and make sure there is no danger of writing past the allocated space. If necessary, truncate all input strings to a reasonable length before passing them to the copy and concatenation functions.
Operation, Build and Compilation: Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code. Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking. For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
Operation: Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment. For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].
Implementation: Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.

CWE-772: Missing Release of Resource after Effective Lifetime

The product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed.

How to prevent it

Requirements: Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, languages such as Java, Ruby, and Lisp perform automatic garbage collection that releases memory for objects that have been deallocated.
Implementation: It is good practice to be responsible for freeing all resources you allocate and to be consistent with how and where you free resources in a function. If you allocate resources that you intend to free upon completion of the function, you must be sure to free the resources at all exit points for that function including error conditions.
Operation, Architecture and Design: Use resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).

References

Advisories

Packages

cs.opensource.google/go/x/crypto

Timeline

May 22, 2026 Published
Sep 23, 2026 Last updated by the source
Oct 31, 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-rm3j-f69w-wqmq golang.org/x/crypto vulnerable to infinite loop on large channel writes	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

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