CVE-2026-33930: Apache Traffic Server Buffer Overflow Flaw

CVE-2026-33930 Overview

CVE-2026-33930 is a stack-based buffer overflow [CWE-121] in Apache Traffic Server. The proxy copies the client Host header into a fixed-size stack buffer during redirect handling without bounds checking. An attacker who sends an over-long Host header can overflow the stack when redirect following is enabled.

The flaw affects Apache Traffic Server 8.0.0 through 8.1.9, 9.0.0 through 9.2.14, and 10.0.0 through 10.1.3. The Apache Software Foundation released fixed versions 9.2.15 and 10.1.4. Exploitation requires only a network-reachable proxy configured to follow redirects.

Critical Impact
A remote, unauthenticated attacker can overflow the stack of the proxy process, causing service crashes and potentially memory corruption during redirect handling.

Affected Products

Apache Traffic Server 8.0.0 through 8.1.9
Apache Traffic Server 9.0.0 through 9.2.14
Apache Traffic Server 10.0.0 through 10.1.3

Discovery Timeline

2026-07-29 - CVE-2026-33930 published to NVD
2026-07-30 - Last updated in NVD database

Technical Details for CVE-2026-33930

Vulnerability Analysis

Apache Traffic Server is a high-performance forward and reverse HTTP proxy. When the proxy is configured to follow HTTP redirects, it re-processes the request against the redirect target. During this handling path, the code copies the client-supplied Host header into a stack-allocated buffer of fixed size. The copy operation does not enforce the destination buffer length.

An attacker who controls the Host header can supply a value larger than the destination buffer. The excess bytes overwrite adjacent stack frame data, including saved return addresses and local variables. This corruption produces a denial-of-service condition and, depending on compiler mitigations and memory layout, may enable further exploitation.

Root Cause

The root cause is an unbounded string copy [CWE-121] into a fixed-size stack buffer inside the redirect-following code path. The developer assumed the Host header would fit the buffer and omitted an explicit length check or bounded copy primitive such as strncpy with a guarded terminator.

Attack Vector

Exploitation requires a Traffic Server instance with redirect following enabled and reachable from the attacker over the network. The attacker sends an HTTP request whose Host header exceeds the fixed buffer size. When the proxy processes a redirect response, the vulnerable copy executes and overflows the stack. No authentication or user interaction is required.

Specific offsets, buffer size, and gadget availability are not documented in the public advisory. See the Apache Security Mailing List Thread for the vendor announcement.

Detection Methods for CVE-2026-33930

Indicators of Compromise

Traffic Server traffic_server process crashes or unexpected restarts recorded in traffic.out or systemd journal logs.
HTTP request logs containing Host header values of abnormal length, often several kilobytes or more.
Segmentation faults or stack corruption traces in core dumps generated by the proxy process.
Sudden gaps in proxy telemetry that correlate with inbound requests carrying malformed Host headers.

Detection Strategies

Inspect HTTP access logs for Host header lengths that exceed normal DNS name limits, typically over 253 characters.
Alert on repeated traffic_server crashes within short windows, particularly on hosts running vulnerable versions.
Deploy a web application firewall or reverse proxy rule in front of Traffic Server to reject requests whose Host header exceeds a sane maximum.

Monitoring Recommendations

Ingest Traffic Server access and error logs into your SIEM and build correlations between long Host headers and process restarts.
Track the running version of Apache Traffic Server across the fleet and flag any host on 8.x, 9.x below 9.2.15, or 10.x below 10.1.4.
Monitor upstream redirect responses since exploitation requires the proxy to enter the redirect-following code path.

How to Mitigate CVE-2026-33930

Immediate Actions Required

Upgrade Apache Traffic Server to version 9.2.15 or 10.1.4, which contain the vendor fix.
If immediate upgrade is not possible, disable redirect following in the proxy configuration to remove the vulnerable code path.
Place a filtering layer in front of the proxy that rejects HTTP requests with excessively long Host headers.
Audit exposed Traffic Server instances and remove direct internet exposure where the service is not required externally.

Patch Information

The Apache Software Foundation released fixed builds 9.2.15 and 10.1.4. Users on the 8.x branch are not listed as receiving a fix and should migrate to a supported release. Refer to the Apache Security Mailing List Thread for release notes and download links.

Workarounds

Disable redirect following in records.config by setting proxy.config.http.redirect_use_orig_cache_key and related redirect options to prevent the proxy from re-processing redirect targets.
Enforce a maximum HTTP header size at the edge using an upstream reverse proxy or WAF, limiting Host to standard DNS name length.
Restrict inbound traffic to Traffic Server to trusted sources where redirects are controlled.

bash

# Configuration example: cap header sizes at the edge (nginx front proxy)
large_client_header_buffers 4 1k;
client_header_buffer_size 1k;

# Optional: reject requests with abnormally long Host headers
if ($host ~* ".{256,}") { return 400; }