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High severity7.5NVD Advisory· Published Jun 8, 2026· Updated Jun 8, 2026

CVE-2026-34356

CVE-2026-34356

Description

Apache HTTP Server 2.4.x is vulnerable to a heap-based buffer overflow when using specific ProxyPassReverseCookie directives with malicious backend servers.

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

Apache HTTP Server 2.4.x is vulnerable to a heap-based buffer overflow when using specific ProxyPassReverseCookie directives with malicious backend servers.

Vulnerability

A heap-based buffer overflow vulnerability exists in Apache HTTP Server, specifically when using the ProxyPassReverseCookie and related directives in conjunction with malicious backend servers. This issue affects versions 2.4.0 through 2.4.67.

Exploitation

An attacker can exploit this vulnerability by configuring a malicious backend server that interacts with the Apache HTTP Server. The vulnerability is triggered when Apache processes specific ProxyPassReverseCookie* directives, potentially leading to the overflow.

Impact

Successful exploitation of this heap-based buffer overflow could lead to a crash of the Apache HTTP Server process or potentially allow an attacker to execute arbitrary code with the privileges of the Apache HTTP Server process.

Mitigation

Users are recommended to upgrade to Apache HTTP Server version 2.4.68, which was released on 2026-06-08 and includes a fix for this issue [1].

References
  1. Apache HTTP Server 2.4 vulnerabilities

AI Insight generated on Jun 8, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected products

1

Patches

1
35c6e405390e

cookie reqest header counting (#324)

https://github.com/icing/mod_h2Stefan EissingMay 27, 2026via body-scan
commit
1 file changed · +4 −0
  • mod_http2/h2_util.c+4 −0 modified
    @@ -1708,6 +1708,8 @@ static apr_status_t req_add_header(apr_table_t *headers, apr_pool_t *pool,
              && !ap_cstr_casecmpn("cookie", (const char *)nv->name, nv->namelen)) {
         existing = apr_table_get(headers, "cookie");
         if (existing) {
+            if (!nv->valuelen)
+                return APR_SUCCESS;
             /* Cookie header come separately in HTTP/2, but need
              * to be merged by "; " (instead of default ", ")
              */
@@ -1719,6 +1721,8 @@ static apr_status_t req_add_header(apr_table_t *headers, apr_pool_t *pool,
             apr_table_setn(headers, "Cookie",
                            apr_psprintf(pool, "%s; %.*s", existing,
                                         (int)nv->valuelen, nv->value));
+            /* Treat the merge as an "add" to not escape LimitRequestFields */
+            *pwas_added = 1;
             return APR_SUCCESS;
         }
     }

Vulnerability mechanics

No source-code context for this CVE — mechanics is only generated when we can read the actual fix diff. Without that, the four sections (root cause, attack vector, affected code, fix) would be speculation rather than analysis.

References

1

News mentions

1