CVE-2026-77411: RabbitMQ amqp091-go: Protocol Desynchronization and Frame Injection via Integer Overflow in readLongstr

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.5%, percentile 44: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 44% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes github.com/rabbitmq/amqp091-go (Go) < 1.13.0, fixed in 1.13.0. Check your lockfile, including transitive dependencies.

What it is

RabbitMQ amqp091-go is a Go AMQP 0.9.1 client. Prior to 1.13.0, readLongstr in read.go returns an empty string and a nil error when a declared AMQP longstr length exceeds 0x7FFFFFFF instead of returning ErrSyntax. The function leaves the declared field bytes unread, while readTable treats the operation as successful and continues parsing from the wrong offset. A malicious or compromised broker can provide an oversized longstr in a table field and desynchronize subsequent AMQP parsing, causing attacker-controlled trailing bytes to be interpreted as later fields or frames and disrupting connection integrity and availability. This issue is fixed in version 1.13.0.

From the GitHub advisory

Summary

A critical stream desynchronization vulnerability has been identified in the AMQP wire-protocol parser. When parsing a long string (readLongstr) within a table field, providing a length that exceeds the maximum signed 32-bit integer (2^31 - 1, or roughly 2.1 GiB) triggers an improper error-handling condition. The parser abruptly aborts the read and returns a success status ("",nil) without consuming the specified bytes from the underlying network buffer. This causes all subsequent read operations to become misaligned. The parser interprets arbitrary offsets within the remaining payload bytes as valid AMQP frame headers, leading to potential Remote Code Execution (RCE), data injection, or complete connection hijacking.

Vulnerability Details

The vulnerability exists within the bounds-checking logic of the readLongstr function:

When length evaluates to a value greater than 0x7FFFFFFF:

Weakness type: CWE-754.

Product: github.com/rabbitmq/amqp091-go (Go) · Assigned by: GitHub_M · Published: 2026-09-16

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: present (depends on deployment conditions)
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.52% probability of exploitation activity in the next 30 days; percentile 44.

Timeline

• 2026-09-16 — CVE record last updated
• 2026-09-16 — CVE record published by GitHub_M
• 2026-09-17 — GitHub-reviewed advisory GHSA-c5pq-fr2g-9jpf published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-c5pq-fr2g-9jpf github.com
2. CVE.org record CVE-2026-77411 cve.org
3. NVD entry CVE-2026-77411 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

Critical Go advisories · Today’s Security Digest