CVE-2026-42499 Quadratic string concatenation in consumePhrase in net/mail
Attackers can cause denial of service in applications using the Go net/mail package by providing pathological email address inputs.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42499?
CVE-2026-42499 is a high-severity denial of service vulnerability in Golang Go, published on 7 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Pathological inputs could cause DoS through consumePhrase when parsing an email address according to RFC 5322.
Weakness: CWE-1046
Which versions are affected by CVE-2026-42499?
2 open source packages ship an affected version, including golang and stdlib. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
golang Bitnami | All versions | 1.25.10, 1.26.3 |
stdlib Go | All versions | 1.25.10, 1.26.3 |
Linux distribution packages (12)
golang1.25 Red Hat:hummingbird:1 | All versions | 0:1.25.10-2.2.hum1 |
golang1.25-bin Red Hat:hummingbird:1 | All versions | 0:1.25.10-2.2.hum1 |
golang1.25-docs Red Hat:hummingbird:1 | All versions | 0:1.25.10-2.2.hum1 |
golang1.25-misc Red Hat:hummingbird:1 | All versions | 0:1.25.10-2.2.hum1 |
golang1.25-src Red Hat:hummingbird:1 | All versions | 0:1.25.10-2.2.hum1 |
golang1.25-tests Red Hat:hummingbird:1 | All versions | 0:1.25.10-2.2.hum1 |
golang1.26 Red Hat:hummingbird:1 | All versions | 0:1.26.3-2.2.hum1 |
golang1.26-bin Red Hat:hummingbird:1 | All versions | 0:1.26.3-2.2.hum1 |
golang1.26-docs Red Hat:hummingbird:1 | All versions | 0:1.26.3-2.2.hum1 |
golang1.26-misc Red Hat:hummingbird:1 | All versions | 0:1.26.3-2.2.hum1 |
golang1.26-src Red Hat:hummingbird:1 | All versions | 0:1.26.3-2.2.hum1 |
golang1.26-tests Red Hat:hummingbird:1 | All versions | 0:1.26.3-2.2.hum1 |
Products include Golang Go.
How do I fix CVE-2026-42499?
Upgrade golang to a fixed version for your release line: 1.25.10 or 1.26.3.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-42499 being exploited?
There is no known exploitation of CVE-2026-42499 in the wild and no public exploit code.
Other vulnerabilities in Golang Go
- CVE-2020-0601 Microsoft Windows CryptoAPI Spoofing
- CVE-2026-27143 Missing bound checks can lead to memory corruption in safe Go in cmd/compile
- CVE-2024-24790 Unexpected behavior from Is methods for IPv4-mapped IPv6 addresses in net/netip
- CVE-2023-39320 Arbitrary code execution via go.mod toolchain directive in cmd/go
- CVE-2023-24540 Improper handling of JavaScript whitespace in html/template
Sources
Also known as AZL-98757, BELL-CVE-2026-42499, BIT-golang-2026-42499, CLEANSTART-2026-AE50754, CLEANSTART-2026-EF06318, CLEANSTART-2026-GQ93723 and 809 more.